Knowledge Bank

Four mineral forms within harzburgite of the Leucite Hills, Wyoming were analyzed using an electron microprobe:

1. phlogopite xenoliths 2)phlogopite crystals within vesicles
2. clinopyroxene phenocrysts
3. olivene xenoliths. The two phlogopite forms are chemically distinct. The xenoliths are rich in Mg, but low in Ti, AI, and Fe compared to the vesicles which are very high in Ti and AI. The lack of Ti in the xenoliths indicates that this phlogopite form was not crystalized from the lava that formed the phlogopites formed within the vesicles. Parallels in the chemical composition of the phlogopite xenoliths and olivine xenoliths indicate that the phlogopite xenoliths may have formed in the upper mantle. The phlogopite crystals within the vesicles of the harzburgite are chemically similar to phlogopite phenocrysts formed from the lavas. However, the vesicle crystals show higher concentrations of Ti, AI, and Fe compared to phenocrysts analyzed by Barton (1979) and The other forms likely crystallized from the lava.