M725 Bismuth Crystals Natural bismuth crystals are extremely rare. These were grown in a laboratory in Florida. Bismuth forms fascinating patterns when it crystallizes and is heavier than lead. The crystals vary in color and have an iridescent sheen. Chemical impurities such as iron, manganese, magnesium, zinc or cobalt cause calcite to be many different colors.
Calcite is polymorphic to aragonite.
They both contain the same elements but have a different crystal structure, which was caused by different environmental conditions when the crystallization took place. Stalagmites and stalactites are formed from calcium-rich ground water seeping through caves. The calcium may be deposited in the form of calcite, or if the growth is forming near a hot spring, it may grow aragonite crystals instead. Calcite is mined for its calcium content. It is used as a base for cement.