WADSLEYITE, NATURAL beta -(Mg,Fe)2SiO4 FROM THE PEACE RIVER METEORITE.

Wadsleyite, a new mineral species, occurs as a fine-grained material in fragments within a vein in the Peace River meteorite (Alberta); it was formed by a series of polymorphic phase transformations, from olivine and ringwoodite, during an extraterrestrial shock event. Wadsleyite has the structure of the beta -phase polymorph of (Mg,Fe)//2SiO//4 and an ideal composition of (Mg//1//. //5Fe//0//. //5)SiO//4. Single crystals of wadsleyite rarely exceed 5 mu m in diameter; polycrystalline aggregates are transparent with a pale fawn coloration and a bulk index of refraction of 1. 76. Wadsleyite is orthorhombic with a 5. 70(2), b 11. 51(7), c 8. 24(4) A, V 541(3) A**3, Z equals 8 and, on the basis of the ideal formula, has a calculated density of 3. 84 g cm** minus **3. All observed X-ray and electron-diffraction data are compatible with space group Imma.