Selenite from Castrillo del Val, Spain

Selenite from Castrillo del Val, Castrillo del Val, Provincia de Burgos, Castilla y León, Spain

Magnificent specimens of Gypsum var Selenite from Castrillo del Val. The seller I bought these from referred to them as arrowheads and I definitely agree.

They're quite opaque and included as selenite goes, but lets be honest, the shape is the thing here. This is a result of a phenomenon called twinning, where a crystal grows with its atoms oriented differently in one half than the other - I believe the technical term for these specimens is 'swallowtail twinning', but it might also be referred to as fishtail twinning.