TOURETITE, A NEW BORATE MINERAL FROM MADAGASCAR

Touretite, LiAl4Be4(B11Be)O28, is a borate mineral found in the Ambalabe granitic pegmatite, Madagascar. The mineral, which is the Li-rich analogue of londonite and rhodizite, occurs as white to pinkish rhombic-dodecahedral crystals reaching 1 cm in diameter, and deposited on tourmalines, feldspars, and heavily corroded spodumene and danburite. The streak is white, the lustre vitreous, and touretite does not show any fluorescence under short wave (254 nm) or long wave (366 nm) ultraviolet light. The Mohs hardness is 8, cleavage is absent, the tenacity is brittle, the fracture is conchoidal, and the measured density is 3.06(1) g/cm 3. Optically, touretite is colorless, isotropic, non-pleochroic, and shows an index of refraction of n = 1.6952  0.0005 (measured using a light source of 589 nm wavelength).