Meteorite Minerals: Extraterrestrial Treasures

Meteorites are among the most scientifically significant materials available for study on Earth. These fragments of asteroids, the Moon, and Mars carry minerals that formed in environments utterly unlike anything found in terrestrial geology — subjecting them to extreme pressures, temperatures, and chemical conditions that produce mineral species impossible or vanishingly rare on Earth's surface.

The mineral assemblage of a meteorite is one of the primary tools scientists use to determine its origin and history. Iron meteorites, composed largely of iron-nickel alloy, display a distinctive intergrowth pattern called Widmanstätten pattern (or Thomson structure) when cut and etched with acid. This pattern — of interlocking bands of kamacite and taenite (two iron-nickel alloy phases) — forms only during extremely slow cooling over millions of years in the parent asteroid's core. It is impossible to reproduce artificially at this scale and is therefore an infallible authentication test.

Silicate minerals in chondrites — the most common type of meteorite — include olivine, pyroxene, plagioclase, and a suite of high-pressure phases that tell stories of violent collisions in the early solar system. Stishovite, a high-pressure polymorph of quartz (SiO2), forms at pressures exceeding 10 gigapascals and is found in meteorites and at terrestrial impact craters, but not in normal geological settings. Its presence in a rock is strong evidence of an impact or extraterrestrial origin.

Ringwoodite is a high-pressure olivine polymorph (Mg,Fe)2SiO4 that was first synthesized in the laboratory, then predicted to exist in Earth's transition zone at depths of 520–660 kilometers. It was eventually found as microscopic inclusions in meteorites, and in 2014 a tiny specimen was confirmed within a diamond brought up from Earth's mantle — providing the first direct evidence of water in the deep mantle. The mineral is named for Australian geochemist Ted Ringwood, who predicted its existence.

Pallasites are among the most visually stunning of all meteorites. They consist of a network of iron-nickel metal surrounding crystals of olivine — sometimes of gem quality (peridot from space). The olivine crystals in pallasites, when translucent and yellow-green, can be faceted as gemstones. The origin of pallasites is debated, but the leading hypothesis is that they formed at the core-mantle boundary of differentiated asteroids. The Esquel pallasite from Argentina, the Fukang pallasite from China, and the Brenham pallasite from Kansas are among the most celebrated examples.

Lunar meteorites — fragments of the Moon's crust ejected by asteroid impacts and subsequently captured by Earth's gravity — contain a distinctive mineral assemblage reflecting the Moon's geological history. The lunar highlands are dominated by anorthosite, a rock composed almost entirely of calcium plagioclase feldspar (anorthite). The lunar maria are basaltic, with pyroxene, olivine, and ilmenite (iron titanium oxide). A mineral found in lunar samples — tranquillityite (Fe8(Zr,Y)2Ti3Si3O24) — was for decades believed to be unique to the Moon. It was finally identified in terrestrial rocks in 2012, in ancient basalts from Western Australia, though it remains exceedingly rare on Earth.

Martian meteorites (the SNC group — shergottites, nakhlites, and chassignites) are igneous rocks crystallized from Martian magma. They contain minerals reflecting a basaltic volcanic history: pyroxenes, olivine, plagioclase, and iron oxides. The nakhlites contain evidence of liquid water that flowed through cracks in the rock on Mars, depositing secondary carbonates and clay minerals. These hydrothermal minerals, formed in the presence of Martian water, are of intense scientific interest as potential environments for ancient microbial life.

For collectors, genuine meteorites represent a tangible connection to the cosmos. The Meteoritical Society maintains the Meteoritical Bulletin, an official registry of authenticated meteorites, which provides provenance documentation essential for establishing authenticity. Reputable dealers provide documentation traceable to this registry, and buyers should be wary of meteorites lacking such documentation.