Rare or unusual gemstones, generally meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite and red beryl.
12.
Titanian chondrodite has been found as inclusions in olivine in serpentinite in West Greenland, where it is associated with clinohumite, olivine, magnesite, magnetite and Ni-Co-Pb sulfides in a matrix of antigorite.
13.
Clinohumite's transparency ranges from transparent to translucent; its nm ) is as follows : ? 1.631; ? 1.638 & ndash; 1.647; ? 1.668;, with a maximum birefringence of 0.028 ( biaxial positive ).
