👉 The term "schriesheimite" is a mineralogy term used to describe a type of quartz crystal. Schriesheimite is a gray or black-colored quartz crystal with a smooth, unstructured texture and is often associated with the volcanic rock schrieß in Germany. Schriesheimite crystals are known for their unique optical properties. They have a high refractive index (c) of 1.546-1.590, which makes them highly reflective. This