Calcite
Calcite is a mineral species commonly found in various rock and mineral collections due to its diverse range of physical properties and appearances. It belongs to the trigonal crystal system and has a chemical formula of CaCO3, making it a calcium carbonate mineral. Calcite exhibits a variety of colors such as white, gray, brown, yellow, green, red, pink, and blue, often with beautiful iridescence or opalescence due to the presence of impurities. It can occur in different crystal habits, including rhombohedrons, scalenohedrons, prisms, and masses, which are highly sought after by collectors for their unique shapes and patterns. Calcite is known for its ability to form pseudomorphs, where one mineral replaces another while retaining the original crystal shape. These minerals can be found in various environments such as sedimentary rocks, hydrothermal veins, limestone caves, and geodes.