A Geoscience Digital Image Library

TitleThin section of quartz monzonite porphyry
DescriptionQuartz monzonite porphyry thin section in coss polarized light. The 3 essential felsic species occur in 2 sizes. The larger plagioclases are euhedral, zoned phenocrysts and in places, glomerporphritic. A few large subhedral kaolinized orthoclase grains are prsent, as are large quartz anhedra. These are set in a poorly defined groundmass of variable grained quartz, orhtoclase, plagioclase, biotite and hornblende. Of these, the mafics are subhedral, the plagioclase is euhedral, the others anhedral. The hornblende is more strongly altered than biotite, which is variably colored in pale green, bluish green, and buff. It is replaced by chlorite and epidote. Acccessories are magnetite, apatite, sphene, and zircon.
LocationUSA ▹ Colorado ▹ Chaffee. Near Garfield.
PhotographerDarla Sondrol. 2002-03-24.
CollectionWard’s Collection of Classic North American Rocks #6.
Key wordsmonzonite, porphyry, Colorado
Tech details726 KB. Thin section. Nikon FDX-35.
GeoDIL number2536