Black Minerals In Granite

The small black specks in the granite above are likely small amphibole grains.

Black minerals in granite.

Granite is the most common intrusive rock in earth s continental crust it is familiar as a mottled pink white gray and black ornamental stone it is coarse to medium grained. Color variation is a response to the percent of each mineral found in the sample. The black grains can be biotite or hornblende. Crystals are common with striated faces shaped in octahedrons or dodecahedrons.

It is about two inches across. Look for a black streak and a strong attraction to a magnet. White granite is a granite that is composed primarily of quartz milky white and feldspar opaque white minerals. It may be gray black or have a rusty coating.

Granite is high in quartz about 25 feldspar and mica. That light background color is punctuated by the darker accessory minerals. Its three main minerals are feldspar quartz and mica which occur as silvery muscovite or dark biotite or both. The pink grains are orthoclase feldspar and the clear to smoky grains are quartz or muscovite.

The quartz and feldspar generally give granite a light color ranging from pinkish to white. Thus classic granite has a salt and pepper look. Magnetite or lodestone is a common accessory mineral in coarse grained igneous rocks and metamorphic rocks. The most common accessory minerals are the black mica biotite and the black amphibole hornblende.

The specimen above is a typical granite.