The depicted specimens are from the Santa Eulalia Mining District in Chihuahua, Mexico, a mining area preferred for silver, zinc, lead, copper and iron. The dog tooth calcite is found there as a mineral deposit in caverns or caves - there is a technical term which is speleothem or cave mineral - and in veins and cracks in the rock, where out from a calcareous solution, over the time the crystals are growing. Depending on different amounts of ore elements the crystals bare colors ranging from transparent and white, to gray, brown, reddish and black.

The low hardness 3 according to the Mohs scale means that the crystal could be scratched with a copper coin - who would like to try it out?