Allendeite

Allendeite, Sc₄Zr₃O₁₂, is an oxide mineral.[1] Allendeite was discovered in a small ultrarefractory inclusion within the Allende meteorite.[1] This inclusion has been named ACM-1.[1] It is one of several scandium rich minerals that have been found in meteorites.[1] Allendeite is trigonal, with a calculated density of 4.84 g/cm³.[1] The new mineral was found along with hexamolybdenum.[1] These minerals, are believed to demonstrate conditions during the early stages of the Solar System, as is the case with many CV3 carbonaceous chondrites such as the Allende meteorite.[1] It is named after the Allende meteorite that fell in 1969 near Pueblito de Allende, Chihuahua, Mexico.[1]

Allendeite
General
Category	Oxide minerals
Formula (repeating unit)	Sc4Zr3O12
Dana classification	4.6.8. Simple oxides
Crystal system	Trigonal
Crystal class	Rhombohedral (3) H–M Symbol: (3)
Space group	R3
Unit cell	a = 9.396, c = 8.720 [Å] V = 666.7 Å^3
Identification
Crystal habit	Microscopic crystals, inclusions
Specific gravity	4.84 (calculated)
Refractive index	2.14 (calculated)
References	[1][2][3]

Occurrence

Allendeite was found as nano-crystals in an ultrarefractory inclusion in the Allende meteorite.[1] The Allende meteorite has shown to be full of new minerals, after nearly forty years it has produced one in ten of the now known minerals in meteorites.[1] This CV3 carbonaceous chondrite was the largest ever recovered on earth and is referred to as the best-studied meteorite in history.[1] The inclusion has only been viewed via electron microscopy.[1] The sample is one centimeter in diameter and has been entrusted to the Smithsonian Institution's National Museum of Natural History with the catalog number USNM7554.[1] One crystal studied is a single 15 x 25 micron size with included perovskite, various osmium-iridium-molybdenum-tungsten alloys, and scandium-stabilized tazheranite.[1] In fact, all allendeite was in contact with perovskite.[1] The grains are anhedral, with no observable crystal forms or twinning.[1]

Significance

Various scandium rich minerals have been found in meteorites, including; davisite, panguite, kangite, tazheranite, thortveitite, and eringaite.[1] Of these, allendeite is the most Sc rich, with only pretulite containing substantially more scandium.[1]

Appearance

Color, streak, luster, hardness, tenacity, cleavage, fracture, density, and refractive index could not be observed because the grain size was too small and the section bearing the mineral was optically thick.[1]

See also

• Classification of minerals
• List of minerals

References

1. Beckett, John R. and Rossman, George R. = Allendeite (Sc₄Zr₃O₁₂ and hexamolybdenum (Mo, Ru, Fe), two new minerals from an ultrarefractory inclusion from the Allende meteorite. American Mineralogist, Volume 99, pages 654-666, 2014. doi:10.2138/am.2014.4667
2. Allendeite data on Mindat.org
3. Allendeite data on Webmin