Inorganic 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, CaAl2O4. The only known natural occurrence of this mineral is in a grossite-rich Fragment of foreign (xeno-) material enclosed within the primary matrix of a rock or meteorite. Click on Term to Read More in the Rare carbonaceous chondrite class that is chemically very close to the CRs and CBs as evidenced by the CH/CBb meteorite Isheyevo. The "H" stands for "high metal" since the CH chondrites contain up to 15 vol. % Fe-Ni metal. The first CH chondrite was found in the Antarctic Allan Hills Click on Term to Read More NWA 470 (Ivanova et al., 2002).
From the abstract:
Natural calcium monoaluminate, CaAl2O4, has been found in a grossite-rich calcium-aluminum-rich inclusion (CAI) from the CH chondrite Northwest Africa 470. The calcium monoaluminate occurs as colorless ~10 mm subhedral grains intergrown with Calcium 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, Term 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, and Group 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. Nebular condensation is the most likely origin for the precursor materials of this Sub-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, but calculations suggest that dust/gas ratios substantially enhanced over solar are required to stabilize CaAl2O4.
Some or all content above used with permission from J. H. Wittke.