Refractory Phases

PART V

REFRACTORY PHASES

CONTINUE TO
[PART I] ChondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More
[PART II] Achondrites
[PART III] Irons
[PART IV] Stony-Irons
[PART VI] Trends for Classification
[APPENDECTOMY]

Solar nebulaThe primitive gas and dust cloud around the Sun from which planetary materials formed. refractory metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn Click on Term to Read More (W, Re, Os, Ir, Mo, Ru, Pt, and Rh) with high vaporization temperatures in excess of ~1620K were the first solids to condense as a single alloyMetal-like substance produced by mixing two or more metals or by the mixture of a metal and another substance. Ceramics can also be mixed to form alloys. A binary alloy contains two components; a ternary alloy contains three. Click on Term to Read More near the midplane of the hot, primordial, pre-stellar coreIn the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. Click on Term to Read More outward to ~3 AUThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The Click on Term to Read More during the rapid infall stage which began over 4.568 b.y. ago (Liffman et al., 2012). These first metal condensates are now present within sub-micron-sized refractory metal nuggets, which likely formed as precipitates of a silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the liquid during rapid quenching (~ 700–1000°C/40 s) under reducingOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons,  while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More conditions (Schwander et al., 2015). Thereafter, these metal nuggets might have served as nucleation sites for later phases such as spinelMg-Al oxide, MgAl2O4, found in CAIs. or meliliteGroup of minerals found in the CAIs of meteorites such as CV chondrites. Melilite consists almost exclusively of the binary solid solution gehlenite (Ca2Al2SiO7) – åkermanite (Ca2MgSi2O7). The melilite in CAIs is closer to gehlenite in composition. The first-formed (highest-temperature) melilite crystallizing from a melt is relatively aluminum-rich and becomes progressively Click on Term to Read More, minerals that became major constituents of CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More. Solar refractory metal nuggets also occur as large, isolated opaque assemblages within primitive carbonaceous meteorites, initially referred to as Fremdlinge, while presolar refractory metal nuggets have been discovered hosted in presolar graphiteOpaque form of carbon (C) found in some iron and ordinary chondrites and in ureilite meteorites. Each C atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, α (hexagonal) and β (rhombohedral), have Click on Term to Read More grains within primitive meteorites, thought to be primary condensateIn the solar nebula, product of a chemical condensation reaction where a mineral phase precipitates (condenses) directly from a cooling vapor. Click on Term to Read More assemblages after Type II supernovae and low-metallicity AGB starsStars on the Asymptotic Giant Branch, which represents a late stage of stellar evolution that all stars with initial masses < 8 Msun go through. At this late stage of stellar evolution, gas and dust are lifted off the stellar surface by massive winds that transfer material to the interstellar Click on Term to Read More (Croat et al., 2013). The solar nebulaAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive Click on Term to Read More refractory metal nuggets are thought to have formed relatively fast (~100 years) during an interval of ~100,000 years, at a temperature of 1440–1616K and a pressure of 100 dyne/cm²; these conditions were created during periods of low accretionAccumulation of smaller objects into progressively larger bodies in the solar nebula leading to the eventual formation of asteroids, planetesimals and planets. The earliest accretion of the smallest particles was due to Van der Waals and electromagnetic forces. Further accretion continued by relatively low-velocity collisions of smaller bodies in the Click on Term to Read More by the proto-Sun (Schwander et al., 2011).

Condensation of other refractory phases (oxides and silicates with vaporization temperatures in excess of ~1350K) followed. In regions of solar composition, mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous Click on Term to Read More condensation progressed in the following sequence: corundumCrystalline form of aluminium oxide, Al2O3, found in Ca-Al-rich inclusions (CAIs). Corundum-bearing  CAI are a rare class of high-temperature condensates from the inner regions of the protoplanetary disk¹. Click on Term to Read More ⇒ hiboniteRefractory mineral, Ca-aluminate (CaAl12O19) that occurs in terrestrial metamorphic rocks and in CAIs of many chondrites. Meteoritic hibonite tends to be blue as seen in the meteorite Isheyevo (Ch/CB). Hibonite is one of the most refractory minerals found in primitive meteorites. Click on Term to Read More ⇒ grossiteCalcium aluminate, CaAl4O7, first found in metamorphosed Israeli limestone and recently in CAIs in CV3 and CR-CH-CB carbonaceous chondrites. Click on Term to Read More ⇒ perovskiteTerm applied to A2+B4+O3 high-pressure minerals with a perovskite structure (general formula ABX3) where "A" is a metal that forms large cations such as Mg, Fe or Ca, "B" is another metal that forms smaller cations such as Si (called silicate perovskite), Ti and to a lesser degree Al, and Click on Term to Read More ⇒ melilite ⇒ spinel ⇒ diopside ⇒ forsteritePure* magnesium end-member (Mg2SiO4) of the olivine solid solution series and an important mineral in meteorites. When magnesium (Mg) is completely substituted by iron, it yields the the pure Fe-olivine end member, fayalite (Fe2SiO4). The various Fe and Mg substitutions between these two end-members are described based on their forsteritic (Fo) Click on Term to Read More ⇒ enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3). Click on Term to Read More. This equilibriumTerm used to describe physical or chemical stasis. Physical equilibrium may be divided into two types: static and dynamic. Static equilibrium occurs when the components of forces and torques acting in one direction are balanced by components of forces and torques acting in the opposite direction. A system in static Click on Term to Read More condensation sequence is most closely exemplified in refractory inclusionInclusions found predominantly in carbonaceous chondrites and are rich in refractory elements particularly calcium, aluminum and titanium that in various combinations form minerals such as spinel, melilite, perovskite and hibonite. There are two types of refractory inclusion: • Ca Al-rich inclusions (CAIs) • Amoeboid olivine aggregates (AOAs) Refractory inclusions were Click on Term to Read More 31-2 in the CO3.00 chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More DOM 08006 (Simon et al., 2019).
Condensation phase relations at various temperatures, pressures, and gas:dust ratios
Photo credit: Ebel, D. S. (2006), Condensaton of rocky material in astrophysical environments.
In Meteorites and the Early Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. II, D. Lauretta et al., editors.
University of Arizona in Tucson. pp. 253–277, + four color plates (after plates 1 and 4). The condensation of these refractory minerals and the formation of calcium–aluminum-rich inclusions (CAIs) occurred during the time interval between 70 t.y. and 2.5 m.y. after the beginning of the rapid infall stage (Mishra and Chaussidon, 2011); a precise age for CAISub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More formation of 4.5672 (±0.0006) b.y. was obtained by Amelin et al. (2002). During this time interval, radiogenic 26Al was introduced into the solar nebula by one or more supernovae (Ciesla and Yang, 2010). A number of independent chronometric studies (e.g., Budde et al., 2018) have demonstrated a concordance in Al–Mg and Hf–W ages for CV CAIs, CV chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at  ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More, CR chondrules, and angrites (D’Orbigny and Sahara 99555), which attests to a homogeneous distribution of 26Al during the first ~4–5 m.y. of solar systemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with history.

At a heliocentricCentered around a sun. Our own Solar System is centered around the Sun so that all planets such as Earth orbit around the Sun. Note that 25% of Americans incorrectly believe the Sun revolves around the Earth. Click on Term to Read More distance corresponding to the location at which CV- and CK-group carbonaceous chondrites were formed, highly porous, refractory, mm-to-cm-sized dustballs became concentrated with CAIs of similar mass forming 16O-rich accretionary rims (Rubin, 2011). Many of these refractory minerals, specifically those which formed within the initial 160,000 years (commensurate with the lifetime of class 0 protostars), survived (perhaps within planetesimalsHypothetical solid celestial body that accumulated during the last stages of accretion. These bodies, from ~1-100 km in size, formed in the early solar system by accretion of dust (rock) and ice (if present) in the central plane of the solar nebula. Most planetesimals accreted to planets, but many – Click on Term to Read More) as primary condensates of a dust-enhanced (10 × solar gas composition which was 16O-rich: Δ17O ~ –25‰ to –20‰; Simon et al., 2019) nebular gas having properties of variable but low pressure, variable but high temperature, and a reducedOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons,  while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More environment (conditions attested by volatility fractionated REEs). Episodic melting of these CAIs occurred over the next 300,000 years, with some experiencing remelting in the chondrule-forming region at least 900,000 years after initial formation (MacPherson et al., 2010).

Some of the earliest refractory phases (hibonite-bearing) formed prior to the incorporation and mixing of 26Al into the solar nebula and are present in CM chondrites (no resolvable 26Mg excesses; e.g., platy-crystals [PLACs] and blue aggregates [BAGs]), while others do show evidence of in situ 26Al decay (e.g., spinel–hibonite spherules [SHIBs] and CAIs). CAIs are likely the direct condensates or evaporative residues formed from one or more episodes of rapid heating and slow cooling of precursor dust. This process continued over a time span as short as 20–100 t.y. (consistent with an FU-Orionis outburst; see below) (Krot et al., 2009; Wurm and Haack, 2009 and references therein), which is datable by the Hf–W and U–Pb systems to 4.5685 (±0.0003) b.y. ago relative to the angrites D’Orbigny, NWA 4590, and NWA 4801 (Burkhardt et al., 2008; Nyquist et al., 2009). This age is in agreement with that obtained by Pb–Pb and Al–Mg dating methods for a CAI from the CV3 NWA 2364 of 4.5682 b.y. (Bouvier and Wadhwa, 2010). It was calculated that initial nebular condensation processes account for 80% of the refractory elementSubstance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of Click on Term to Read More enrichment (e.g. Ca, Al) in type A and type B CAIs, while 20% is due to the subsequent evaporationProcess in which atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. Click on Term to Read More of more volatile elementsChemical elements that condense (or volatilize) at relatively low temperatures. The opposite of volatile is refractory. Volatile elements can be divided into moderately volatile (Tc = 1230–640 K) and highly volatile (Tc < 640 K). The moderately volatile lithophile elements are: Mn, P, Na, B ,Rb, K, F, Zn. The moderately Click on Term to Read More (e.g. Mg, Si) (Grossman et al., 2008).

Evidence for an early, instantaneous, impact-generated shock waveAbrupt perturbation in the temperature, pressure and density of a solid, liquid or gas, that propagates faster than the speed of sound. origin for CAIs (and chondrules) around large planetesimals has been presented by Sanders (2008) and by Hood and Weidenschilling (2011). This would include an origin associated with bow shocks produced by planetesimal interactions with Jupiter, or more plausibly, an origin within shock zones associated with impact-generated vapor-melt plumes from high-velocity collisions of large planetesimals. Chondrules were melted and slowly cooled within the dusty zone of large planetesimals on a timescale that overlaps the formation of CAIs and which continued for ~2.6 m.y (commensurate with the lifetime of class 1–3 protostars). During that period, some CAIs were transported radially outward into the accretion zones of chondrite parent bodies. If employing the planetesimal nebular shock model, any delay between the formation of CAIs and chondrules may be explained as the time required for the completion of Jupiter’s formation.

Following their formation near the proto-Sun, many of these refractory minerals were transported radially outward by turbulent diffusionMovement of particles from higher chemical potential to lower chemical potential (chemical potential can in most cases of diffusion be represented by a change in concentration). Diffusion, the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena. Because diffusion is thermally activated, coefficients for diffusion Click on Term to Read More mechanisms to chondritic accretionary regions. Others may have been confined to the protoplanetary diskFlattened and rotating disk of dense gas and dust/solids orbiting a young star from which planets can eventually form.   Click on Term to Read More embedded in the center of spiral arms (Haghighipour and Boss, 2003), or possibly transported to cooler heliocentric regions (2–5 AU) by bipolar outflows (x-wind and/or disk winds) or by photophoresis—a force created in response to an ~100-fold increase in the Sun’s luminosityBasic property used to characterize stars, luminosity is defined as the total energy radiated by a star each second. An object’s luminosity is often compared to that of the Sun (Lsun = 4 × 1033 ergs/s = 3.9 × 1026 Watts). Luminosity has the same units as power (energy per Click on Term to Read More during an FU-Orionis outburst resulting from an enhanced accretion rate within ~1 AU of the central starSelf-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars. (Wurm and Haack, 2009). When cm-sized CAIs are fully illuminated in an optically thin region of the disk, they are transported vertically and radially outward along the surface of the (flared) protoplanetary disk following a temperature gradient from hot to cold. Calculations show that CAIs measuring up to 1 cm in size, representing a total mass of 0.005 Earth masses, could have been easily transported to the asteroid beltBelt located between 2.12 and 3.3 AU from the Sun and located between the orbits of Mars and Jupiter containing the vast majority of asteroids. The asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such Click on Term to Read More at a distance of ~3 AU, and some may have exceeded 10 AU. Here the condensation sequence was arrested, and these minerals remained stable against gas drag and the accretionary influence of the SunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the for at least 1 m.y. Eventually, they rained down to the nebular midplane and ultimately coalesced with newly forming chondrules to form the nascent chondritic planetesimals. Very ancient ages have been measured for some iron meteorites and for the ungroupedModifying term used to describe meteorites that are mineralogically and/or chemically unique and defy classification into the group or sub-group they most closely resemble. Some examples include Ungrouped Achondrite (achondrite-ung), Ungrouped Chondrite (chondrite-ung), Ungrouped Iron (iron-ung), and Ungrouped Carbonaceous (C-ung). Click on Term to Read More basaltic meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More Asuka 881394, with the latter having an age of 4.56675 (±0.00031) b.y. based on the 238U/235U ratio of 137.88, or 4.56557 (±0.00055) b.y. based on the newly refined 238U/235U ratio of 137.768 (±0.038) (Amelin et al., 2014; Wimpenny et al., 2013; Koefoed et al., 2015). These similar ancient ages indicate that their respective parent bodies accreted contemporaneously with CAI formation (Wadhwa et al., 2009). Schematic of the Evolution of the Early Solar System
A. Giant Molecular CloudAn interstellar gas cloud that is dense enough to allow the formation of molecules and comprised of a cold dense complex mixture of interstellar gas and dust roughly 75% hydrogen and 21-24% helium. Clouds contain trace amounts of other molecules, of which well over 100 different types have now been Click on Term to Read More ⇒ B. Protostars ⇒ C. Proto-Sun and Protoplanetary Disk

click on photo for a magnified view

Diagram credit: Van Kooten et al., PNAS, vol. 113, no. 8 (2016, open access link)
‘Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites’
(https://doi.org/10.1073/pnas.1518183113) CAIs are particularly abundant in the CV-group of carbonaceous chondrites, but they also occur in many other carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than Click on Term to Read More groups, in K chondrites, in ordinary chondrites, and in enstatite chondrites, and they have been identified in cometConglomeration of frozen water and gases (methane, ammonia, CO2) and silicates that that formed in the outer solar system and orbits the Sun. In recent years, the description of comets has shifted from dirty snowballs to snowy dirtballs with more dust than ice. However, the ratio is less than 10-to-1. Click on Term to Read More samples (81P/Wild-2) from NASA’s STARDUST missionSpace mission to study Comet Wild 2 (see http://stardust.jpl.nasa.gov/home/index.html). During the encounter, Stardust performed a variety of tasks including making counts of particles encountered by the spacecraft and real-time analyses of the compositions of these particles and volatiles. It also captured cometary particles using Aerogel and stored them for return. Wark–Lovering monomineralic rims commonly occur on most all CAI types, providing evidence of episodic flash heating events in a more oxidizingOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons,  while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More environment of the solar nebula; these energetic events are often cited as being associated with magnetic reconnectiion flares. These events resulted in volatilization of Mg, Si, and Ca from the outermost layer of CAIs, followed by the diffusion of elements (possibly derived from accetionary forsterite dust which is texturally and mineralogically similar to AOAMillimeter sized, fine-grained inclusions present to a few volume-percent in most carbonaceous chondrites. They can be round but can also be irregularly shaped like an amoeba (thus the name amoeboid). They are forsterite (Mg-rich olivine) and Ca-Al-Ti mineral aggregates. The most characteristic texture of AOAs is an anorthite core (sometimes Click on Term to Read More forsterite) back onto the surface of the CAIs. Alternatively, the formation of Wark–Lovering rims may be attributed to relatively slow evaporation from solid CAIs. Additional information on CAI formation can be found on the Allende page.

Ebert et al. (2018) investigated the Ti isotopeOne of two or more atoms with the same atomic number (Z), but different mass (A). For example, hydrogen has three isotopes: ¹H, ²H (deuterium), and ³H (tritium). Different isotopes of a given element have different numbers of neutrons in the nucleus. Click on Term to Read More systematics of CAIs and Na–Al-rich chondrules from ordinary and CO chondrites. CAIs from both of these chondrite groups show the presence of nucleosynthetic anomalies, such as an average excess in ε50Ti of ~9. On the other hand, although Na–Al-rich chondrules in the CO chondrites studied have a ε50Ti excess, those from the ordinary chondrites do not. Given that Na–Al-rich chondrules from both CO and ordinary chondrites are considered to have incorporated refractory components (~30–80% CAIs and/or AOAs), they reason that the refractory material precursor to ordinary chondrules did not have a ε50Ti excess, and thus was different from the refractory material admixed to form CO chondrules. They contend that this difference may be due to the specific formation region of the respective precursor refractory material: either in the non-carbonaceous (NC) region within the inner Solar System (ordinary chondrites), or in the carbonaceous (CC) region beyond Jupiter (CO chondrites). They propose that the rare CAIs with ε50Ti excesses which are present in ordinary chondrites could represent the smaller-sized CAIs (<150 µm) that were able to migrate across Jupiter’s gap in the protoplanetary disk (see diagram below). Schematic of the Transportation and Distribution of CAIs in the Early Solar System

click on photo for a magnified view

Diagram credit: Ebert et al., EPSL, vol. 498 p. 263 (2018)
‘Ti isotopic evidence for a non-CAI refractory component in the inner Solar System’
(https://doi.org/10.1016/j.epsl.2018.06.040) CAIs were originally grouped as ‘coarse-grained’ and ‘fine-grained’ inclusions (Grossman, 1975). However, continued studies have led to further refinement in their classification, with an emphasis on those from the CV group. Coarse-grained CAIs have been classified into three main groups (A, B, and C) based primarily on the proportions of fassaite and melilite, the latter corresponding to the series with Ca-rich end member åkermanite and Al-rich end member gehlenite. Other characteristic phases include spinel, hibonite, perovskite, and anorthiteRare compositional variety of plagioclase and the calcium end-member of the plagioclase feldspar mineral series with the formula CaAl2Si2O8. Anorthite is found in mafic igneous rocks such as anorthosite. Anorthite is abundant on the Moon and in lunar meteorites. However, anorthite is very rare on Earth since it weathers rapidly Click on Term to Read More.
NWA 2086, CV3R, 46 g end section with large (the largest known?) CAI
Photo courtesy of Dr. Martin Horejsi
See the complete story of this CAI as published in Meteorite Times Magazine—The Accretion Desk.

COARSE-GRAINED CAIs

• Type A Inclusions:

• Compact
• refractory elementsUsing research by Wood (2019), any of the elements with a relatively high condensation temperature of 1291 K < TC,50 < 1806 K in the solar nebula1. They are the first elements to condense out of a cooling gas. Refractory elements are the main building blocks of rocky planets, dwarf Click on Term to Read More (proto-CAIs) initially crystallized from a melt following evaporation of nebular dust and gas in the earliest stages of solar system evolution
• inclusions are composed of an aggregate of compositionally similar proto-CAIs that were rapidly coagulated
• rounded inclusions contain coarse-grained melilite (Åk 1–80), spinel, perovskite, and the pyroxenes fassaite (Al–Ti-diopside) and rhönite
• minerals typically 16O-rich
• Fluffy
• unmelted but have experienced varying degrees of recrystallization
• aggregates of refractory elements (proto-CAIs) formed by gas–solid condensation from a solar composition gas
• irregular shape
• contain melilite (Åk 0–36), V-rich spinel, hibonite, and perovskite (the latter sometimes with associated pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category. Click on Term to Read More)
• melilite may be altered to secondary phases such as andradite after accretion within a planetesimal
• minerals typically 16O-rich

• Type B Inclusions:
  

1. crystallized from partially molten droplets in which some evaporation occurred
2. unique to CV chondritesMeteorite class named after the Vigarano meteorite that fell in Italy in 1910. They have abundant large, well-defined rimless (?) chondrules of magnesium-rich olivine (~0.7 mm diameter; 40-65 vol. %), often surrounded by iron sulfide. They also contain 7-20 vol. % CAIs. The often dark-gray matrix is dominated by Fe-rich Click on Term to Read More; formed in the CV region by clumping of type A CAIs, incorporation of dust, and melting (Rubin, 2011)
3. generally depleted in Si and Mg from evaporation compared to type A CAIs
4. less refractory than type A CAIs
5. many experienced complex alteration histories
6. large sizes (~5–25 mm) due to continued incorporation of forsterite dust and multiple melting events
7. contain melilite (Åk1–74), fassaite (sometimes with associated Fremdlinge (now known as opaque assemblages, which are refractory metal-rich objects formed as early nebular condensates), spinel (including palisade bodies and framboids), anorthite, perovskite, and forsterite
8. three divisions of type B inclusions have been adopted, which reflect a continuum:
• B1
• inclusions are zoned, consisting of melilite and spinel, with the cpx fassaite along with glass existing at their interface; the fassaite and glass are residues after rapid evaporation of Mg and Si from the primary melt
• coarser-grained than B2 inclusions
• crystallized rapidly from early, homogeneous melts
• composition of melilite varies (Åk30–65 in the core, Åk20–35 in the rim)
• melilite has variable O-isotopic compositions
• B2
• inclusions are unzoned and lack melilite-rich mantles
• melilite is zoned with a compositional range of Åk45–90
• more silica-rich compositions than B1
• higher anorthite/gehlenite ratios than B1
• crystallized slowly from evolved, isolated melt pockets
• B3 (forsterite-bearing)
• uncommon inclusionFragment of foreign (xeno-) material enclosed within the primary matrix of a rock or meteorite. Click on Term to Read More type (found only in CV and CB chondrites) that contains forsteritic olivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion Click on Term to Read More (Fo93–100, up to 45 vol%)
• precursor material was AOA-like
• spinel, forsterite, and pyroxene cores are 16O-rich; melilite and anorthite mantles are 16O-depleted
• cores crystallized from partial to complete melts; mantles have an evaporative origin
• less refractory than other CAIs due to Mg and SiO evaporation
• melilite in zoned inclusions may have variable compositions (Åk12–100)
• melilite has a compositional range of Åk6–90 and is commonly altered to secondary phases such as nepheline

Type C Inclusions:

• crystallized from partially molten droplets possibly related to fine-grained, spinel-rich CAI precursor material, with the addition of altered CAI Type B inclusions
• high volatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). element contents suggest melting under high pressures or high dust/gas ratios
• coarse-grained with diverse textures and mineralogies
• melilite has wide ranges, but typically Åk40–50
• contain abundant anorthite (38–60 vol%), along with fassaite and spinel, but are deficient in forsterite
• minerals are typically 16O-poor due to O-isotopic exchange during melting and assimilation of dust in an 16O-poor reservoir of the nebula, or through isotopic exchange on the parent asteroid
• CV3 (Allende) exhibits asteroidal isotopic exchange during metasomatic alteration of melilite to secondary phases such as grossular, nepheline, sodalite, hedenbergite, and andradite
• considered to be a precursor component in the condensation origin of Al-rich chondrules (those containing >10 wt% Al₂O₃)

FINE-GRAINED, SPINEL-RICH CAIs:

• rimmed, concentrically-zoned structure
• nebular condensate origin with a multi-stage formation history
• composed primarily of spinel at their cores and mantles of melilite, along with Al-diopside or fassaite, anorthite, nepheline, and salite
• melilite mostly altered to secondary phases such as andradite and grossular

AMOEBOID OLIVINE AGGREGATES (AOAs)

• olivine-rich objects present in most grouped and ungrouped carbonaceous chondrites, and have been found in an LL3.0 ordinary chondriteWork in Progress Ordinary chondrites (OCs) are the largest meteorite clan, comprising approximately 87% of the global collection and 78% of all falls (Meteoritical Society database 2018)1. Meteorites & the Early Solar System: page 581 section 6.1 OC of type 5 or 6 with an apparent shock stage of S1, Click on Term to Read More
• the least refractory fine-grained inclusions
• irregularly-shaped, mm- to cm-sized, porous or compact, sintered and annealed aggregates of high-temperature (~1200–1384K), 16O-rich, solar nebular condensates
• originated by fractional condensation or fractional vaporization in an 16O-rich reservoir
• rapid cooling occurred at an estimated rate of >0.02K/hr at a nebular pressure of 0.0001 barUnit of pressure equal to 100 kPa.
• porous AOA olivines contain low CaO and high MnO and CrO concentrations indicative of slow accretion and rapid cooling of nebular forsterite through disequilibrium condensation
• compact AOA olivines contain higher CaO and lower MnO and CrO concentrations indicative of reheating of porous AOAs, or rapid accretion and slow cooling of nebular forsterite
• compact AOAs likely formed closer to the Sun than porous AOAs
• likely formed in the same region as CAIs but experienced cooler condensation temperatures (Fagan et al., 2004)
• alternatively, but not strongly supported, formation occurred from rapidly cooled igneous melts (Wasson et al., 2004)
• composed primarily of forsteritic olivine and a refractory component composed of the high-Ca pyroxene Al-Ti-diopside, along with anorthite, spinel, CAIs, and rare melilite; secondary nepheline, sodalite, and other phases may be present as a result of aqueous alteration processes on the parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More (Fagan et al., 2003)
• FeNi-metal is rare, indicating rapid extraction from the condensation site following forsterite condensation
• AOA olivine was a precursor to chondruleRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at  ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More olivine; AOAs may provide a genetic link between CAIs and low-FeO type-I chondrules via metasomatic processing (Krot et al., 2004) in which low-Ca pyroxene shells have accreted and melting has occurred within less 16O-rich, chondrule-forming nebular regions (Krot et al., 2005; Ruzicka et al., 2011)
• may be associated with formation of ordinary, rumuruti, and enstatite chondriteType of meteorite high in the mineral enstatite and also referred to as E-chondrites. Although they contain substantial amounts of Fe, it is in the form of Ni-Fe metal or sulfide rather than as oxides in silicates. Their highly reduced nature indicates that they formed in an area of the Click on Term to Read More groups through removal of varying amounts of AOA fractionate from an initial CI-like composition

Excellent images of AOAs can be seen in John Kashuba’s article ‘Amoeboid Olivine Aggregates’ published in the November 2015 issue of Meteorite Times Magazine.

FUN CAIs (Fractionated and Unknown Nuclear isotope anomalies)

• rare type of inclusion present in some carbonaceous chondrite groups
• large isotopic anomalies are present for O, Mg, and Si, while nonlinear isotopic anomalies exist for Ca, Sr, Ba, Nd, Sm, Ti, and Cr
• anomalies resulted from the mixing of components from normal nucleosynthetic processes (e.g., the r-process in Type Ia SN, type II SN) in unusual proportions
• subsequently subjected to mass fractionationFractionation of isotopes or elements that is dependent on their masses. Click on Term to Read More processes (e.g., Rayleigh distillation), possibly within gaseous protoplanets
• volatility-fractionated REEOften abbreviated as “REE”, these 16 elements include (preceded by their atomic numbers): 21 scandium (Sc), 39 Yttrium (Y) and the 14 elements that comprise the lanthanides excluding 61 Promethium, an extremely rare and radioactive element. These elements show closely related geochemical behaviors associated with their filled 4f atomic orbital. Click on Term to Read More patterns
• abundant spinel and large isotopic fractionations may indicate a higher temperature origin
• magnesium in the inclusions is isotopically heavy
• lack the 26Mg excess that is present in other CAIs, suggesting they formed very early, prior to 26Al incorporation into solar nebula
• they were segregated quickly from the region of solar flareSudden eruptions from the surface of the Sun. Flares typically last a few minutes and can release energies equivalent to millions of hydrogen bombs. Flares become frequent near sunspot maximum, when smaller flares can occur daily and large flares can occur about once a week. During a flare the material irradiation to preserve evidence of the composition of the pristine protosolar molecular cloud
• the group includes some mass fractionated hibonite inclusions with or without nucleosynthetic anomalies

µCAIs (Bland et al., 2007)

• a distinct population of µm-sized CAI inclusions; not fragments of larger CAIs
• consist of corundum cores with complete Al, Ca-containing rims
• O-isotopic compositions are unique

CAIs are also classified based on REE abundances into Groups I–VI. For example, Group I formed from an essentially unfractionated nebular gas, and Group II formed by condensation of a fractionated nebular gas depleted in an ultra-refractory component (e.g., fine-grained CAIs).

PLACs (platy hibonite crystals)

• rare type of inclusion (60–110 µm) present in CM carbonaceous chondrite groups
• gas–solid nebular condensate which lacks the 26Mg excess present in CAIs
• represent some of the first solids that formed in the solar nebula following the low-velocity impact of a stellar shock front with the protosolar cloud, triggering its collapse
• formed prior to the incorporation and/or homogenization of freshly synthesized short-lived nuclides like 26Al
• formed rapidly over a span of 10,000–100,000 years
• formed prior to CV CAIs having the ‘canonical’ 26Al/27Al initial ratio (5.2 [±0.2] × 10^–5); nuclides would not be manifest in CAIs until a few 100,000 years later
• large nucleosynthetic anomalies are present for Ca, Ti, and Si, which were implanted by interstellar dustGrains of carbon and silicate ~0.1-1.0 mm in size. Dust grains are a major component of the interstellar medium. Dust blocks visible light causing interstellar extinction and scatters incident starlight, particularly blue light (which has a wavelength comparable to the dust grain's size), causing reddening. Cooling of interstellar gas and Click on Term to Read More grains
• volatility-fractionated REE patterns
• the short-lived nuclideA nuclear species characterized by Z protons and N neutrons. Click on Term to Read More 41Ca is absent
• formed in a highly 16O-enriched reservoir
• plots more broadly spread about the CCAM (carbonaceous chondrite anhydrous mineral) line relative to SHIBs on an oxygenElement that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only Click on Term to Read More three-isotope diagram (see below)

Diagram credit: Kööp et al., GCA, vol. 184, pg. 164 (2016)
‘New constraints on the relationship between 26Al and oxygen, calcium, and titanium isotopic variation
in the early Solar System from a multielement isotopic study of spinel-hibonite inclusions’
(http://dx.doi.org/10.1016/j.gca.2016.04.018)

SHIBs (spinel–hibonite spherules)

• rare type of hibonite grain (50–100 µm) present in CM carbonaceous chondrite group
• show evidence of in situ decay of 26Al
• early condensates that formed rapidly over a span of 10,000–100,000 years
• most likely formed by late reprocessing ~100,000–700,000 years after CV CAI formation
• formed at lower temperatures than PLACs, in a region already depleted in the most refractory REEs
• O-isotopes more similar to CAIs in CR chondrites and Acfer 094 than to PLACs
• formed in a homogeneous, highly 16O-enriched reservoir
• define a tight cluster along the CCAM (carbonaceous chondrite anhydrous mineral) and PCM (primitive chondrule mixing) lines on an oxygen three-isotope diagram (see below)

Diagram credit: Kööp et al., GCA, vol. 184, pg. 164 (2016)
‘New constraints on the relationship between 26Al and oxygen, calcium, and titanium isotopic variation
in the early Solar System from a multielement isotopic study of spinel-hibonite inclusions’
(http://dx.doi.org/10.1016/j.gca.2016.04.018)

Selected References:

Planetary Materials, Reviews in Mineralogy, J.J. Papike (editor), vol. 36, (1998)

How the Type B1 CAIs Got Their Melilite Mantles, Richter et al., LPSC XXXIII, #1901 (2002)

Oxygen isotopic compositions and origins of calcium–aluminum-rich inclusions and chondrules, E. Scott and A. Krot, MAPS, vol. 36, #10 (2001)

Early solar system events and timescales, G. Lugmair and A. Shukolyukov, MAPS, vol. 36, #8 (2001)

The formation of rims on calcium–aluminum-rich inclusions: Step I–Flash heating, D. Wark and W. Boynton, MAPS, vol. 36, #8 (2001)

Precursors of Type C inclusions—Evidences from the new kind of anorthite–spinel-rich inclusions in the Ningqiang carbonaceous chondrite, Y. Lin and M. Kimura, LPSC XXVIII, #1067 (1997)

A Comprehensive Study of Pristine, Fine-grained, Spinel-rich Inclusions from the Leoville and Efremovka CV3 Chondrites, I: PetrologyScience dealing with the origin, history, occurrence, chemical composition, structure and classification of rocks. Click on Term to Read More, MacPherson et al., LPSC XXXIII, #1526 (2002)

Making Calcium–Aluminum-rich Inclusions and Chondrules near the Young Sun by Flares, F. Shu et al., MAPS, vol. 35, suppl. (2000)

On the Remelting of Type B Calcium–Aluminum-rich Inclusions, H. Connolly and D. Burnett, MAPS, vol. 35, suppl. (2000)

TEM study of compact Type A Ca,Al-rich inclusions from CV3 chondrites: Clues to their origin, A. Greshake et al., MAPS, vol. 33, #1 (1998)

In situ formation of palisade bodies in Ca,Al-rich refractory inclusionsInclusions found predominantly in carbonaceous chondrites and are rich in refractory elements particularly calcium, aluminum and titanium that in various combinations form minerals such as spinel, melilite, perovskite and hibonite. There are two types of refractory inclusion: • Ca Al-rich inclusions (CAIs) • Amoeboid olivine aggregates (AOAs) Refractory inclusions were Click on Term to Read More, S. Simon and L. Grossman, MeteoriticsScience involved in the study of meteorites and related materials. Meteoritics are closely connected to cosmochemistry, mineralogy and geochemistry. A scientist that specializes in meteoritics is called a meteoriticist. Click on Term to Read More, vol. 32 (1997)

The origin of type C inclusions from carbonaceous chondrites, J. Beckett and L. Grossman, EPSL, vol. 89, #1 (1988)

Mineralogy and petrography of amoeboid olivine aggregatesMillimeter sized, fine-grained inclusions present to a few volume-percent in most carbonaceous chondrites. They can be round but can also be irregularly shaped like an amoeba (thus the name amoeboid). They are forsterite (Mg-rich olivine) and Ca-Al-Ti mineral aggregates. The most characteristic texture of AOAs is an anorthite core (sometimes Click on Term to Read More from the reduced CV3 chondrites Efremovka, Leoville and Vigarano: Products of nebular condensation, accretion and annealing, M. Komatsu et al., MAPS, vol. 36, #5 (2001)

Insights into the Formation of Type B2 Refractory Inclusions, S. Simon and L. Grossman, LPSC XXXIV, #1796 (2003)

The identification of meteorite inclusions with isotope anomalies, D. Papanastassiou and C. Brigham, Astrophysical Journal, vol. 338 (1989)

The origin of the ‘FUN’ anomalies and the high temperature inclusions in the Allende meteorite, G. Consolmagno and A. Cameron, Moon and the Planets, vol. 23 (1980)

Isotopic Heterogeneity and Correlated Isotope FractionationConcentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process. Click on Term to Read More in Purple FUN Inclusions, C. Brigham et al., LPSC Abstracts, vol 19 (1988)

On the origin of the Ca–Ti–Cr isotopic anomalies in the inclusion EK-1-4-1 of the Allende-meteorite, K. Kratz et al., Memorie della Società Astronomica Italiana, vol. 72, #2 (2001)

Type C CAIs: New Insights Into Early Solar System Processes, A. Krot et al., 67th Annual Meteoritical Society Meeting, #5042 (2004)

Formation of Chondritic refractory inclusions: the astrophysical setting, J. Wood, GCA, vol. 68, #19 (2004)

Evaporation of cmas-liquids under reducing conditions: constraints on the formation of type B1 CAIs, A. Davis et al., NIPR International Symposium (2003)

TEM/SEM Evidence for residual melt inclusions in type B1 CAIs, J. Paque et al., LPSC XXXVIII, #1755 (2007)

Type C Ca,Al-rich inclusions from Allende: Evidence for multistage formation, A. Krot et al., GCA, vol. 71, #18 (2007)

The White Angel: A unique wollastonite-bearing, mass-fractionated refractory inclusion from the Leoville CV3 carbonaceous chondrite, C. Cailet Komorowski et al., MAPS, vol. 42, #7/8 (2007)

Primordial compositions of refractory inclusions, L. Grossman et al., GCA, vol. 72 (2008)

Oxygen isotopic compositions of Allende Type C CAIs: Evidence for isotopic exchange during nebular melting and asteroidal metamorphism, A. Krot et al., GCA, vol. 72 (2008)

Nebular history of amoeboid olivine aggregates, N. Sugiura et al., MAPS, vol. 44, #4 (2009)

Origin and Chronology of Chondritic Components: A Review, A. Krot et al., GCA, vol. 73 (2009)

Refractory Phases in Primitive Meteorites Devoid of 26Al and 41Ca: Representative Samples of First Solar System Solids?, S. Sahijpal and J. Goswami, The Astrophysical Journal, vol. 509 (1998)

Isotopic records in CM hibonites: Implications for timescales of mixing of isotope reservoirs in the solar nebula, Liu et al., GCA, vol. 73 (2009)

Amoeboid olivine aggregates (AOAs) in the Efremovka, Leoville, and Vigarano (CV3) chondrites: A record of condensate evolution in the solar nebula, Ruzicka et al., GCA, vol. 79 (2012)

Forsterite-bearing type B refractory inclusions from CV3 chondrites: From aggregates to volatilized melt droplets, Bullock et al., MAPS, vol. 47, #12 (2012)

New constraints on the relationship between 26Al and oxygen, calcium, and titanium isotopic variation in the early Solar System from a multielement isotopic study of spinel-hibonite inclusions, Kööp et al., GCA, vol. 184 (2016)

PSRD article by G. Jeffrey Taylor: ‘Dating Transient Heating Events in the Solar Protoplanetary Disk‘, November 16, 2012

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CONTINUE TO
[PART I] Chondrites
[PART II] Achondrites
[PART III] Irons
[PART IV] Stony-Irons
[PART VI] Trends for Classification
[APPENDECTOMY]

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© 1997–2019 by David Weir