Some typical occurrences of the rock-forming feldspars


Some typical occurrences of the rock-forming feldspars

Table
Some typical occurrences
of the rock-forming feldspars
Potassium feldspars*
sanidine potassium-rich volcanic rocks and near-surface minor intrusions—e.g., rhyolites, trachytes, and high-temperature contact metamorphic rocks
orthoclase potassium-rich dike rocks—e.g., rhyolite and trachyte porphyries; granites, granodiorites, and syenites**; moderate- to high-grade metamorphic gneisses and schists; and sandstones
microcline granitic pegmatites, hydrothermal veins; granites, granodiorites, and syenites**; low- to moderate-grade metamorphic rocks; sandstones and conglomerates
Plagioclase feldspars
albite granites; granitic pegmatites; low-grade metamorphic gneisses and schists; sandstones
oligoclase granodiorites and monzonites; sandstones; moderate-grade metamorphic rocks
andesine diorites; andesites; moderate-grade meta-morphic rocks, especially amphibolites
labradorite gabbros and anorthosites***; diabases and basalts
bytownite gabbros and anorthosites***; diabases and basalts
anorthite gabbros; contact-metamorphosed impure limestones; and high-grade metamorphic rocks
*Including perthites. In addition, anorthoclase occurs only in a few rather abnormal syenites (e.g., larvikite), and adularia—transparent, colourless to white, commonly opalescent potassium feldspar with a pseudo rhombohedral habit—occurs in some low-temperature hydrothermal veins. **Typical syenites consist of nearly 90 percent alkali feldspar. ***Typical anorthosites consist of about 90 percent plagioclase feldspar.
See as table:

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Universalium. 2010.

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