M487 - Staurolite Crystals in Schist Matrix, Russia.

Basic silicate of iron and aluminum, often with some magnesium and
zinc. Hardness 7 to 7-1/2. Monoclinic crystals in twins, intergrown at
nearly 60 degrees. Commonly called "fairy cross". Russia The
right-angled staurolite penetration twins are popular as good luck
charms. Transparent single crystals are occasionally cut into gems.

From Russia.