Association reaction in forsterite under shock compression.

Transmission electron microscopic observation of forsterite (Mg(2)SiO(4)) shocked to peak pressures of 78 to 92 gigapascals revealed that forsterite breaks down to an assemblage of MgO plus MgSiO(3) glass. This strongly supports the interpretation that the high-pressure phase of forsterite under shock compression is due to the assemblage of MgSiO(3) perovskite plus MgO.

Pyrrhotites: Stoichiometric Compounds with Composition Fen--1Sn (nge8).

A new type of natural pyrrhotite, orthorhombic 11C type (a = 6.892, b = 11.952, c = 5.744 x 11 angstroms), and the hexagonal 6C type (a = 6.89, c = 5.76 x 6 angstroms) are described. Their compositions are Fe(10)S(11) and Fe(11)S(12), respectively. Pyrrhotites stable in nature have essentially stoichiometric composition, Fe(n)-(l)S(n) (n>/=8), with the structures of n/2C type for n even and of nC type for n odd. The solid solutions between Fe(11)S(12) and Fe(10)S(11), and between Fe(10)S(11) and Fe(9)S(10) are considered metastable in nature.

Modified spinel, Beta-manganous orthogermanate: stability and crystal structure.

A new high-pressure polymorph with a modified spinel structure, beta-Mn(2)GeO(4), is stable in a pressure range intermediate between the field of the polymorph with the olivine structure and that of another high-pressure polymorph. Oxygen atoms are located approximately in cubic close packing with manganese and germanium atoms in octahedral and tetrahedral interstices, respectively, as in the spinel structure; however, germanium atoms form Ge(2)O(7) groups instead of isolated GeO(4) groups.