Hornblende

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Hornblende refers to a field and classroom name for a range of dark-colored amphibole minerals found in many types of igneous and metamorphic rocks. These minerals exhibit varying chemical compositions, yet they all share the common trait of being double-chain inosilicates with very similar physical properties. As a rock-forming mineral, hornblende plays a crucial role as an essential constituent in acidic and intermediate igneous rocks such as granite, diorite, syenite, andesite, and rhyolite. It is also commonly found in metamorphic rocks like gneiss and schist. Some rocks are comprised almost entirely of hornblende. The group of hornblende minerals can be easily identified due to their dark color (usually black) and two distinct directions of excellent cleavage that intersect at 124 and 56 degrees. Source: https://www.mindat.org/min-1930.html, https://geology.com/minerals/hornblende.shtml