Greisen is a highly altered granitic rock or pegmatite, usually composed predominantly of quartz and micas (mostly muscovite). Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic-hydrothermal alteration related to the late-stage release of volatiles dissolved in a magma during the ...

greisen, modification of granite, an intrusive igneous rock; it consists essentially of quartz and white mica (muscovite) and is characterized by the absence of feldspar and biotite.

Greisen is a hydrothermally metamorphosed granitic rock. It is composed mostly of light-colored mica (muscovite, lepidolite, zinnwaldite) and quartz. Greisen with cassiterite from Namibia. Width of sample 10 cm. It is a type of endoskarn.

The term greisen refers to an assemblage of quartz + muscovite, accompanied by varying amounts of other distinctive minerals such as fluorite, topaz and tourmaline. Greisenisation is defined by Shcherba (1970) as the high temperature, post-magmatic alteration of...

A highly variable, low to high-temperature metasomatic rock characterised by the presence of quartz and white mica, commonly with topaz, fluorite, tourmaline and locally with cassiterite, biotite, zinnwaldite, orthoclase, andalusite and diaspore; some contain various sulphides. Typically greisens may host Be, W, Mo, Sn and Ta mineralization.

The greisen, products of hydrothermal alteration and replacement of the veins' wall rock, developed during or immediately following veining. You might find these chapters and articles relevant to this topic. Greisen and vein-type tin-polymetallic ores are found in the western exocontact zone of the Salmi batholith (Fig. 8.10).

The term greisen refers to an assemblage of quartz + muscovite, accompanied by varying amounts of other distinctive minerals such as fluorite, topaz and tourma­ line.

Greisen is a term used originally by miners of Saxony, E Germany for a variety of granite containing only Sn ore, mica, and quartz, and little or no feldspar (von Leonhard, 1823). In modern terms it may be defined as a pneumatolytically altered granite composed mainly of quartz, pale silvery-green mica, and topaz.

May 8, 2018 · greisen An altered, light-coloured, igneous rock consisting of white mica and quartz. The rock forms by the reaction of crystalline granite with hot fluorine-rich vapour derived from the crystallizing granite at a deeper level in the intrusion.

Greisen is a highly altered granitic rock or pegmatite. Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic alteration related to release of volatiles dissolved in a magma during the solidification of that magma.