Biotite is a rock-forming mineral found in a wide range of crystalline igneous rocks such as granite, diorite, gabbro, peridotite, and pegmatite. It also forms under metamorphic conditions when argillaceous rocks are exposed to heat and pressure to form schist and gneiss.

2023年8月26日 · Biotite: Biotite is another dark-colored mineral that is sometimes found in granite, accounting for up to 5% of the rock’s composition. It is a type of mica that gives granite a dark, almost black color.

This sample of granite comes from Luxulyan, St Austell, Cornwall. It is known locally as biotite granite, although the granite actually contains both muscovite and biotite.

— Biotite occurs in coarse-grained granite exposed on the east side of U.S. route 45, near Monico (SW SE sec. 6 T35N.R11E) (Van Schmus, 1980). PORTAGE COUNTY: Biotite is common in the gneisses and tonalites exposed at numerous points in T.23N.

2024年1月4日 · Biotite granite is rich in biotite mica, which gives it a dark color, often in shades of brown or black. This variety is known for its striking appearance and is frequently used in...

2022年4月2日 · Here we present a characterization of biotite and amphibole compositions from S-, I-, and A-type granites. A database of biotite (1215 data points) and amphibole (525 data points) compositions from previously classified S-, I-, and A-type granites has been compiled.

Granite, coarse- or medium-grained intrusive igneous rock that is rich in quartz and feldspar; it is the most common plutonic rock of the Earth’s crust, forming by the cooling of magma (silicate melt) at depth. Learn more about the properties and uses of granite in this article.

A common, widespread, rock-forming mineral, biotite is a significant mineral in granites, diorites, and igneous pegmatites. In pegmatites, biotite crystals can be very large. It also occurs in schists, gneisses, and hornfels that resulted from either regional or contact metamorphism.

In plain light, biotite in a granite appears a slightly drab brown. Radiation damage from zircon can leave pleochroic spots that fade to extinction at a different rate that the surrounding, undamaged material.

This biotite granite features biotite, quartz (note that most of it is about one order too thick, which accounts for the yellowish color), perthite, microcline, plag, and muscovite. Several of the biotite grains include zircon.