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Related to Felsite: Felsitic Texture


A light-colored, fine-grained igneous rock composed chiefly of quartz or feldspar.
A rock characterized by felsitic texture.



a fine-grained acid extrusive rock consisting of potassic feldspar (orthoclase) and quartz. Felsite sometimes contains acid plagioclase and dark minerals, such as pyroxene and biotite. It results from the recrystallization of volcanic glass during diagenesis and the initial phase of metamorphism. Felsitic texture is characteristic of paleotypical rocks such as quartz porphyries, keratophyres, and orthoclase porphyries. The term “felsite” is sometimes emphasized in the name of a rock, for example, felsodacite and felsophyre.

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The main rock-types are ultramafic to mafic, but granites, granophyres and felsites, containing economic tin deposits, fluorite and pegmatite minerals are also present (Cairncross and Dixon, 1995).
Ferguson (1946) and Ferguson and Weeks (1950) subdivided the slate series and felsite into an older unit of andesite, chlorite schist, rhyolite, and felsite, intruded by younger granite and alaskite, and overlain by Carboniferous sedimentary rocks of the Horton Group.
Dunn (1877) described the rock in which the cobalt ores occur as a very fine-grained felsite.
The plutons, dykes, and sills of the Charlo plutonic suite consist of varied intermediate to felsic rock including quartz monzonite to monzogranite, quartz-plagioclase rhyolite porphyry, hornblende dacite porphyry, and felsite.
Box 2, Victor, CO) has a large new supply of sylvanite and calaverite crystals and masses (to several mm) on typical felsite matrix from the Cresson mine, Cripple Creek,Teller County.
In order of decreasing age they are (1) agmatite containing blocks of host rock in a coarse-grained igneous matrix, (2) felsite, rhyolite porphyry, and microgranite, (3) layered and massive gabbro, (4) medium- to coarse-grained amphibolebiotite granite, (5) heterogeneous mafic rocks with a generally dioritic to tonalitic matrix containing schliers and blocks ranging from layered gabbro, to monzonitic, syenitic and granitic varieties.
However, several kilometres along strike to the northeast in the Island Falls quadrangle, a lens of conglomerate, basal to the Shin Brook Formation and as thick as 30 metres, consists of pebbles of felsite, quartzite and slate in a chlorite-rich sandstone matrix (Ekren and Frischknecht 1967).