Felsite


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Related to Felsite: Felsitic Texture

felsite

[′fel‚sīt]
(petrology)
A light-colored, fine-grained igneous rock composed chiefly of quartz or feldspar.
A rock characterized by felsitic texture.

Felsite

 

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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Extensive albitisation is seen along veins, as brecciation, as formation of foliated albititic felsites and chlorite schists, as carbonate-rich albitite, and as large-scale albitite bodies [23, 35].
Albite is the dominant mineral in foliated felsites, in chlorite schist, in carbonate-rich albitite, and in large-scale albitite bodies [23,50].
It includes massive carbonate-rich albitite, brecciated and altered host rock with albite-carbonate groundmass, and foliated albitic felsites. The massive carbonate-rich albitite usually occurs as several-meter thick deposits (Figure 3(d)) with the largest albitite body being more than 150 m wide and 1500 m long (Figure 1(b)).
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).
Several mineralized veins cut across gabbro, granophyres and felsites. The gangue minerals in the veins are quartz and siderite and the primary ore minerals were argentiferous galena, associated with zinc (sphalerite), copper (chalcopyrite) and minor antimony mineralization.
Dunn (1877) described the rock in which the cobalt ores occur as a very fine-grained felsite. Beck (1907) described the country rock not as a quartzite, but as a quartz-feldspar rock with the feldspars largely altered to sericitic mica, however he was not against it being called an aplite.
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.
The upper margin of the granite consists of an almost continuous layer of fine-grained, pink, felsic rock varying from featureless felsite to microgranite with abundant granophyric intergrowth and drusy miarolitic cavities, to rhyolite porphyry that is commonly spherulitic.
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).
1996) along with clasts of quartzite and felsite (Skinner 1974).
However, the provenance of numerous felsite and granite pebbles in the conglomerate is less obvious.