Is slate intrusive or extrusive?
Neither really! Intrusive & Extrusive rocks are a classification of igneous rock types! Slate is a Metamorphic rock formed by heat and pressure from deep inside the earth. Usually it’s origin is a shale-type Sedimentary rock like clay or volcanic ash. Volcanic ash is a form of extrusion from an erupting Volcano. So i guess that makes a slates origin an extrusive rock type, but not slate itself! Slates mineral composition is mainly composed of quartz and muscovite or illite, often along with biotite, chlorite, hematite, and pyrite and, less frequently, apatite, graphite, kaolin, magnetite, tourmaline, or zircon as well as feldspar.
