1.5" Lemon-Yellow Ettringite Crystal Cluster - South Africa

Ettringite is a hydrous calcium aluminum sulfate mineral that typically bears colorless to yellow coloration. It was first described by J. Lehmann in 1874 from an occurance at Ettringer Bellerberg Volcano in Germany, where it formed from metamorphically altered limestone. It can also occur within xenoliths and weathering crusts on larnite. It is important in the setting of Portland cement, where it forms as a result of the reaction between calcium aluminate and calcium sulfate.

Chemical formula - Ca6Al2(SO4)3(OH)12 · 26H2O