Name:   Trachyte

Geologic Name:  None

Reference: Lindgren, Waldemar and Ransome, F.L., Geology and gold 
deposits of the Cripple Creek district, Colorado, U.S. Geol. Survey Prof.
paper 54, p. 77, 1906.

Microscopic characters:   Nearly holocrystalline, the
apparent porphyritic textrure as seen in ordinary light is due to the 
contrasted weathering of the margins of the phenocrysts.  The feldspathic
phenocrysts have a wide range of compositon:  Crypto to micro-perthitic
soda-orthoclase is common.  Another species is anorthoclase.  Biotite and
magnetite are the important accessories.  Serpentine, together with some
chlorite, occurs probably as alteration of augite.  Sericite is very abundant.