Felsite

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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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Sherd Sherd Sherd Grain Surface A7 (#1) A22a (#1) type (1) (#1) Quartz 22 25 22 Plagioclase 9 10 10 K-feldspar 1 1 2 (orthoclase) Opaque 2 2 2 (iron oxide) Chalcedony 3 2 2 (chert) Quartz-mica 1 1 1 tectonite (slate) Glassy VRF 55 53 53 Felsitic VRF 3 3 4 Microlitic VRF 4 3 4 Total VRF (62) (59) (61) Grain Average Standard type (1) (n=3) deviation (2) Quartz 23 2.1-2.2 Plagioclase 10 1.4-1.5 K-feldspar l 0.5-0.7 (orthoclase) Opaque 2 0.7 (iron oxide) Chalcedony 2 0.7-0.9 (chert) Quartz-mica 1 0.5 tectonite (slate) Glassy VRF 54 ~2.5 FelsiticVRF 3 0.9-1.0 Microlitic VRF 4 0.9-1.0 Total VRF (61) (~2.5) (1) VRF = volcanic rock fragments.
The rock is made of quartz phenocrysts (5%), plagioclase (35%) and biotite + hornblende (10%), disseminated in a felsitic groundmass made of potassic feldspar (50%).