Melilite

Group of minerals found in the 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 of meteorites such as 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. 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 magnesium-rich with falling temperature. This is the compositional region of interest for most CAIs (except forsterite-bearing type-B CAIs), and the expected result for an igneous melilite in this range (such as those in type Bs) is a compositionally zoned crystal having an aluminum-rich 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 and magnesium-rich rim.

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