Cassiterite

We seldom see good crystals of Cassiterite from the tin-tungsten deposit at Krásno in the Karlovy Vary Region of the Czech Republic, so this part-stellate repeated twin is a superb find from a recently purchased collection.  Cassiterite, a tin oxide, here forms roughly half of a sixling twin, with one whole and two-part arms of the sixling remaining.  The valleys between each of the three limbs are formed by the sharply defined re-entrant angles of the repeated twinned-pairs.  The coal-black faces are smooth with a bright reflective metallic lustre and in the exposed base can be seen small inclusions of milky Quartz.  A splendid twinned Cassiterite from the old Krásno Sn-W deposit.