Trachyte Porphyry #16

3D Model

This 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. This sample is from Near Cripple Creek, Teller County, Colorado, USA. The specimen is 9 cm across.