Stauralite

Stauralite

Stauralite,  Fe2+2Al9O6(SiO4)4(O,OH)2 is a regional metamorphic neosilicate mineral. It is classed as an index mineral,and is useful in determining the depth, pressure, and temperature at which metamorphism occurs. This specimen displays the characteristic "Stauralite cross". The cross is the result of cruciform penetration twinning of the stauralite crystals..The specimen is from the Kola peninsula, Russia.