A Geoscience Digital Image Library

TitleTrachyte porphyry, Near Cripple Creek, Teller County, Colorado
DescriptionThis very fine grained, porphyritic rock, is a trachyte porphyry. It contains many phenocrysts of feldspar (mostly altered remnants of sanidine), mafic phenocrysts that were amphibole before alteration, and a matrix of plagioclase, orthoclase and minor quartz. Accessory minerals include apatite, titanite (sphene), pyroxene, pyrite and calcite. The specimen is 9 cm across.
ChronostratigraphyTertiary (Post-Oligocene)
LocationUSA ▹ Colorado ▹ Teller. Near Cripple Creek.
PhotographerJoseph Hartman. 2001-02-14.
CollectionWard’s Collection of Classic North American Rocks #16.
Key wordstrachyte, porphyry, Cripple Creek, Colorado
Tech details777 KB. Hand specimen. Fujifilm FinePix S1Pro digital camera; 60mm AF Nikon micro lens.
GeoDIL number77