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The exact nature of tripuhyite remains controversial more than 100 years after the first description of the mineral. Different stoichiometries and crystal structures (rutile or tri-rutile types) have been suggested for this Fe-Sb-oxide. To address these uncertainties, we studied tripuhyite from Tripuhy, Minas Gerais, Brazil (type material) and Falotta, Grisons, Switzerland using single-crystal and powder X-ray diffraction (XRD), optical microscopy and electron microprobe analysis.Electron microprobe analyses showed the Fe/Sb ratios to be close to one in tripuhyite from both localities. Single crystal XRD studies revealed that tripuhyite from the type locality and from Falotta have the rutile structure (P4 2 /mnm, a = 4.625(4) c = 3.059(5) and a = 4.6433(10) c = 3.0815(9) A Ê , respectively). Despite careful examination, no evidence for a tripled c parameter, characteristic of the tri-rutile structure, was found and hence the structure was refined with the rutile model and complete Fe-Sb disorder over the cationic sites in both cases (type material: R 1 = 3.61%; Falotta material: R 1 = 3.96%). The specular reflectance values of type material tripuhyite and lewisite were measured and the following refractive indices calculated (after Koenigsberger): tripuhyite n min = 2.14, n max = 2.27; lewisite (cubic) n = 2.04.These results, together with those of 57 Fe and 121 Sb Mössbauer spectroscopy on natural and synthetic tripuhyites reported in the literature, indicate that the chemical formula of tripuhyite is Fe 3+ Sb 5+ O 4 (FeSbO 4 ). Thus, tripuhyite can no longer be attributed to the tapiolite group of minerals of general type AB 2 O 6 . A comparison of the results presented with the mineralogical data of squawcreekite suggests that tripuhyite and squawcreekite are identical. In consequence, tripuhyite was redefined as Fe 3+ Sb 5+ O 4 with a rutile-type structure. Both the proposed new formula and unit cell (rutile-type) of tripuhyite as well as the discreditation of squawcreekite have been approved by the Commission on New Mineral and Mineral Names (CNMMN) of the International Mineralogical Association (IMA).

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Ganterite, [Ba 0.5 (Na,K) 0.5 ]Al 2 (Si 2.5 Al 1.5 O 10 )(OH) 2 , the barium-dominant analogue of muscovite, was discovered in the crystalline basement rocks of the Berisal Complex, Simplon Region, Switzerland. Examples of this new rock-forming mica are found in bands and lenses of white-mica schist, and in a leucocratic zoisite-celsian gneiss. Samples of the schist, and especially of the celsian-bearing gneiss, are characterized by high whole-rock Ba contents of up to 15 wt.% BaO. The mineral paragenesis consists of zoisite, quartz, plagioclase, apatite, zircon and amphibole in the schist, and zoisite, celsian, quartz, margarite ± armenite in the gneiss. Ganterite is light grey to silver, has a vitreous luster, a perfect {001} cleavage, a laminated fracture, and a flexible tenacity. Mohs hardness, determined from micro-hardness indentations, is 4-4½. The mica is biaxial (-), ␣ 1.600 (calc.), ␤ 1.619, ␥ 1.622, and 2V(meas.) equal to 42.5 ± 2°. The calculated density of the most Ba-rich ganterite is 3.11 g/cm 3 . Single crystals typically are 0.5 by 0.15 mm (or less), and occur in small bands, lenses or clusters 0.5 to 10 cm in thickness. Ganterite is monoclinic, space group C2/c, Z = 4, a 5.212 (1), b 9.046(2), c 19.978(4) Å, ␤ 95°48', V 937.6 Å 3 , corresponding to a 2M 1 polytype. The strongest seven powder-diffraction lines [d in Å(I)(hkl)] are: 2.571(100)(131,202), 2.602(95)(130,131), 1.5054(91)(060,2010), 3.737(77)(023), 3.887(76)(113), 4.481(71)(110), and 3.495(71)(114). The new mineral species is named after the geographical region in which it was found. SOMMAIRELa gantérite [Ba 0.5 (Na,K) 0.5 ]Al 2 (Si 2.5 Al 1.5 O 10 )(OH) 2 , un analogue de la muscovite à dominance de barium, a été découvert au sein du socle cristallin du complexe du Bérisal, dans la région du Simplon, en Suisse. On trouve ce type de mica dans des couches et lentilles de schiste à mica blanc, et des lentilles de gneiss leucocrate à celsiane et zoïsite. Des échantillons de schiste et de gneiss possèdent jusqu'à 15% de BaO (poids). La gantérite coexiste avec zoïsite, celsiane, quartz, plagioclase, apatite, zircon et amphibole au sein du schiste, et zoïsite, celsiane, quartz, margarite ± arménite dans le gneiss. La gantérite est gris-pâle à argenté, elle possède un éclat vitreux, un clivage {001} parfait, une structure lamellaire et une ténacité élastique. La dureté de Mohs, déterminée à partir de micro-indentations de dureté, est de 4-4½. Les indices de réfraction sont ␣ 1.600 (calc.), ␤ 1.619 et ␥ 1.622, et la valeur mesurée de 2V (négatif) est de 42.5 ± 2°. La densité calculée de la gantérite la plus riche en Ba est de 3.11 g/cm 3 . En général, les monocristaux font 0.5 par 0.15 mm (ou moins), et on les trouve au sein de petites couches, lentilles ou agrégats mesurant de 0.5 à 10 cm d'épaisseur. La gantérite est un minéral monoclinique, groupe spatial C2/c, Z = 4; a 5.212(1), b 9.046 (4), c 19.978(4) Å, ␤ 95°48', V 937.6 Å 3 ; il s'agit du polytype 2M 1 . Les sept raies les plus intenses du spectre de diffraction X (méthode des poudres)...

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