Ferridravite, a new mineral of the tourmaline group from Bolivia

Ferridravite, a new member of the tourmaline group, occurs at the San Francisco mine, near Villa Tunari (Alto Chapare), Bolivia, as a rare coating on the schistose country rock. The observed forms are a {1120}, r {l0l l}, andd Q02T). Ferridravite has no cleavage and an uneven fracture. The measured density ot3.26(3) g/cm3 is in good agreement with the calculated value of 3.33 E/cm3. The color is blac$ the streak is brown. The luster is resinous, more or less splendent. Ferridravite is uniaxial (-) with refractive indices e : 1.743(3) and <^r : 1.800(3). Crystallographically, ferridravite is rhombohedral, R3m, with unit-cell parame