👉 Argillite, also known as beryl, is a type of mineral that is formed from the feldspar minerals quartz and hornblende. It is a very hard, brittle form of these minerals, which are found in the Earth's crust. The structure of argillite is composed of layers of quartz and hornblende arranged in a zigzag pattern, known as a "Z" shape. This type of mineral is known for its high refractive index, or the amount of
