Approximately 275 mineral species have been identified in meteorites, reflecting diverse redox environments, and, in some cases, unusual nebular formation conditions. Anhydrous ordinary, carbonaceous and R chondrites contain major olivine, pyroxene and plagioclase; major opaque phases include metallic Fe-Ni, troilite and chromite. Primitive achondrites are mineralogically similar. The highly reduced enstatite chondrites and achondrites contain major enstatite, plagioclase, free silica and kamacite as well as nitrides, a silicide and Ca-, Mg-, Mn-, Na-, Cr-, K- and Ti-rich sulfides. Aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates, complex organic compounds, magnetite, various sulfates and sulfides, and carbonates. In addition to kamacite and taenite, iron meteorites contain carbides, elemental C, nitrides, phosphates, phosphides, chromite and sulfides. Silicate inclusions in IAB/IIICD and lIE iron meteorites consist of mafic silicates, plagioclase and various sulfides, oxides and phosphates. Eucrites, howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides. Ureilttes .are made up mainly of calcic, chromian olivine and low-Ca clinopyroxene embedded in a carbonaceous matrix; accessory phases include the C polymorphs graphite, diamond, lonsdaleite and chaoite as well as metallic Fe-Ni, troilite and halides. Angrites are achondrites rich in fassaitic pyroxene (i.e. , AI-Ti diopside); minor olivine with included magnesian kirschsteinite is also present. Martian meteorites comprise basalts, Iherzolites, a dunite and an orthopyroxenite. Major phases include various pyroxenes and olivine; minor to accessory phases include various sulfides, magnetite, chromite and Ca-phosphates. Lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase. Several meteoritic phases were formed by shock metamorphism. Martensite (a2-fe,Ni) has a distorted body-centered-cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling. The C polymorphs diamond, lonsdaleite and chaoite formed by shock from graphite. Suessite formed in the North Haig ureilite by reduction of Fe and Si (possibly from olivine) via reaction with carbonaceous matrix material. Ringwoodite, the spinel form of (Mg,Fe)2Si04, and majorite, a polymorph of (Mg,Fe)Si03 with the garnet structure, formed inside shock veins in highly shocked ordinary chondrites. Secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hy-. droxides formed directly from metallic Fe-Ni by oxidation, phosphates formed by the alteration of schreibersite, and sulfates formed by alteration of troilite.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.1997.tb01262.x

Mineralogy of meteorite groups

Refractory inclusions in the prototypical CM chondrite, Mighei

The volatile element depletion patterns of planetary size objects and the chemical and isotopic composition of numerous smaller objects such as chondrules and calcium- and aluminum-rich inclusions (CAIs) provide the motivation to consider evaporation and condensation processes in the early solar system. Equilibrium thermodynamic calculations of condensation of phases in the solar nebula provide an important reference with which natural solar system materials can be compared. The theoretical background for fractionation of elemental and isotopic compositions during kinetically controlled evaporation and condensation is explored in some detail. Some parameters can be calculated from first principles, but others must be measured in the laboratory, and a number of evaporation experiments are described and interpreted. Elemental and isotopic fractionations of solar system materials are then intepreted in the context of the theoretical and experimental considerations. A key point is that the processes that led to chondrules and planets appear to have occurred under conditions very close to equilibrium, whereas the processes that led to CAIs involved significant departures from equilibrium.

Condensation and Evaporation of Solar System Materials

Trace element abundances and magnesium, calcium, and titanium isotopic compositions of grossite-containing inclusions from the carbonaceous chondrite Acfer 182

J. M. Dehart

Papers

Low temperature annealing and cathodoluminescence studies of type I chondrule analogs