Staurolite specimens from Kola Peninsula

Staurolite is a common metamorphic mineral that is useful to geologists to determine the degree of metamorphism. Staurolite is famous for its twinned crystals that form into the shape of a cross. Its name comes from the greek for cross. The twin is a classic penetration twin where it appears as if two crystals grew into and out of each other. It actually forms two twin types; one that is nearly 90 degrees and one that is nearly 60 degrees. The 60 degree type is more common but the 90 degree type is the most sought after. It was associated with Christianity as a symbol for the cross and as a good luck charm. It has been given the names "Fairy Stone" or "Fairy Cross". Some scarcer specimens show both twin forms and can look like a blunt six rayed star.