Seifertite Dera P, Prewitt C T, Boctor N Z, Hemley R J American Mineralogist 87 (2002) 1018-1023 Characterization of a high-pressure phase of silica from the Martian meteorite Shergotty alpha-PbO2-like _database_code_amcsd 0002871 4.097 5.0462 4.4946 90 90 90 Pbcn atom x y z Biso Si 0 .1522 .25 .8 O .7336 .6245 .9186 .1