💎 Calcite – A calcium carbonate mineral with the formula CaCO₃, and one of the most common and widespread minerals on Earth. It crystallises in the trigonal system and is the primary component of limestone and marble, as well as a common gangue mineral in many ore deposits. Calcite occurs in a wide variety of habits including scalenohedral ("dogtooth"), rhombohedral, prismatic, fibrous, and massive forms. It ranges in colour from colourless and white to yellow, orange, pink, green, blue, brown,