Dog Tooth Calcite
Dogtooth Calcite, also known as Dogtooth Spar, is a speleothem (a structure formed in a cave by the deposition of minerals from water, e.g. a stalactite or stalagmite) forming through mineral precipitation of water-borne Calcite. It is normally found in limestone caves that consists of very large calcite crystals resembling dog's teeth but can also grow in veins, fractures and geodes. It is basically Calcite in groupings of thick and pointy scalenohedral (a hemihedral crystal form of 8 or 12 faces, each face being a scalene triangle) crystals.