Hornblende

Hornblende is a field and classroom name used for a group of dark-colored amphibole minerals found in many types of igneous and metamorphic rocks. These minerals vary in chemical composition but are all double-chain inosilicates with very similar physical properties. Hornblende is a rock-forming mineral that is an important constituent in acidic and intermediate igneous rocks such as granite, diorite, syenite, andesite, and rhyolite. It is also found in metamorphic rocks such as gneiss and schist. A few rocks consist almost entirely of hornblende. Hornblende minerals as a group are relatively easy to identify. The diagnostic properties are their dark color (usually black) and two directions of excellent cleavage that intersect at 124 and 56 degrees. https://www.mindat.org/min-1930.html https://geology.com/minerals/hornblende.shtml