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Felsic magmas and lavas have lower temperatures of melting and solidification than mafic magmas and lavas. Felsic rocks are usually light in color and have specific gravities less than 3. The most common felsic rock is granite. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars (albite-rich).
Felsite covered with dendritic pyrolusite Dike of felsite on Islay in Scotland. Felsite is a very fine-grained volcanic rock that may or may not contain larger crystals.Felsite is a field term for a light-colored rock that typically requires petrographic examination or chemical analysis for more precise definition.
Quartz monzonite is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock. The plagioclase is typically intermediate to sodic in composition, andesine to oligoclase.
Rhyolite – Igneous, volcanic rock, of felsic (silica-rich) composition Comendite – Hard, peralkaline igneous rock, a type of light blue grey rhyolite; Pantellerite – Peralkaline rhyolite type of volcanic rock; Scoria – Dark vesicular volcanic rock; Shonkinite – Intrusive igneous rock – a plutonic rock
Mafic rocks are primarily composed of biotite, hornblende, pyroxene and olivine. Generally, felsic rocks are light colored and mafic rocks are darker colored. [18] For textural classification, igneous rocks that have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called ...
Alkali feldspar granite, some varieties of which are called 'red granite', [1] is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives the rock a predominant pink to reddish hue; peppered with minor amounts of black minerals. [2] [3]
Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface. It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained or glassy. [5]
Pitchstone is a dark coloured, glassy volcanic rock formed when felsic lava or magma cools quickly. Since it is a volcanic glass, pitchstone may have a conchoidal fracture. Pitchstones may also contain phenocrysts, in which case it is a form of vitrophyre. Pitchstone has a resinous lustre, or silky in some cases, and a variable composition. Its ...