Muonionalusta Meteorites

Iron meteorites are composed primarily of various alloys of iron and nickel, and are derived from molten planetary cores that were broken apart billions of years ago. The crystalline patterns within Meteorites are known as "Windmanstatten patterns". These patterns can only form in the vacuum of space where the molten pieces of planetary cores come into contact with very few molecules to which they can transfer their heat and thereby cool. The large metallic crystals characteristic of meteorites require literally millions of years of cooling to form from a molten planetary core fragment. It has been estimated that it took about 1000 years for these molten pieces of planetary core to cool by just 1 degree celsius! The beautiful crystalline patterns characteristic of meteorites are more than just beautiful oddities-they tell us how long it took for the planetary core from which the meteorite is derived to cool! In a recent volume of Meteoritics & Planetary Science, (vol. 38, no. 11, p.1579-1583) it was reported that Stishovite was found for the first time in an iron meteorite-the Muonionalusta iron.  The following is the abstract from this publication:

"The first occurrence of stishovite in an iron meteorite, Muonionalusta (group IVA), is reported. The mineral occurs intimately mixed with amorphous silica, forming tabular grains up to ~3 mm wide, with a hexagonal outline. It was identified using X-ray diffraction and Raman microspectroscopy. The unit-cell parameters of stishovite are a = 4.165(3) Å and c = 2.661(6) Å, and its chemical composition is nearly pure SiO2. Raman spectra show relatively sharp bands at 231 and 754 cm-1 and a broad band with an asymmetric shape and a maximum around 500 cm-1. The rare grains are found within troilite nodules together with chromite, daubreelite, and schreibersite. From their composition and morphology, and by comparisons with silica inclusions in, e.g., the Gibeon IVA iron, we conclude that these rare grains represent pseudomorphs after tridymite. The presence of stishovite in Muonionalusta is suggested to reflect shock metamorphic conditions in the IVA parent asteroid during a cosmic impact event."