Name:   Andesite Porphyry

Geologic Name:  None

Reference: Worcester, P.G., The geology of the Ward region Boulder County,
Colorado:  Colorado Geol. Survey Bull. 21, p. 43-44, 1920.

Microscopic characters:  Porphyritic texture with phenocrysts of plagioclase
and a few of hornblende in a very fine confused goundmass.  The plagioclase
phenocrysts are somewhat clouded due to alteration and show irregular albite
twinning.  In a few instances they show zonal development.  The hornblende
phenocrysts are partially altered to chlorite and calcite.  The groundmass is a
fine irregular aggregate of quartz, orthoclase, plagioclase and green hornblende
with abundant secondary epidote, chlorite and clacite.  There are also
abundant magnetite grains and a few crystals of apatite.