[en] Touretite, LiAl 4 Be 4 (B 11 Be)O 28 , 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 is deposited on tourmalines, feldspars, and heavily corroded spodumene and danburite. The streak is white, the luster 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 ¼ 1.6952 6 0.0005 (measured using a light source of 589 nm wavelength). The empirical formula, calculated on the basis of 28 oxygen atoms per formula unit from the chemical analysis determined by LA-TOF-ICP-MS, is (Li 0.38 Cs 0.24 K 0.14 Rb 0.03 Na 0.02 Pb 0.01 & 0.18) R1.00 (Al 4.00 Si 0.05 Fe 2þ 0.03 Mn 0.02) R4.10 (Be 3.60 Li 0.40) R4.00 (B 11.28 Be 0.72) R12.00 O 28. The cubic unit-cell parameters, determined by single-crystal X-ray diffraction
Disciplines :
Earth sciences & physical geography
Author, co-author :
Hatert, Frédéric ; Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Depret, Martin ; Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Bomal, Florent ; Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Pezzotta, Federico
Vignola, Pietro ; Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Wälle, Markus
Lefevre, Pierre ; Université de Liège - ULiège > Département de géologie
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