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The article reports the 66 letters that make up the correspondence between A. Daubrée and Q. Sella. The letters written by Daubrée (38) and by Sella (28) are kept at the Fondazione Sella o.n.l.u.s.(Biella) and the library of the Institut de France (Paris), respectively. The topics are mainly related to positions of president, in the order, of the Institut de France (Daubrée) and of the Accademia Nazionale dei Lincei, which Sella reorganized after Rome became the capital of Italy in 1871. In particular, Sella, to enhance the scientific role of Italy, supports Italian candidates worthy of becoming members of the Institut. At the same time Sella, who had to abandon his promising crystallographic research in favour of politics but aspires to be elected member of the Académie des Sciences himself, highlights his relationship with the international mineralogical community and his promotion of the Italian scientific activity., Rivista di Storia dell'Università di Torino, Vol 11 No 2 (2022)

Laurentthomasite, ideally Mg2K(Be2Al)Si12O30, is a new milarite-group member found within quartz-syenite pegmatites from the Ihorombe region, Fianarantsoa Province, Madagascar. It occurs as euhedral {0001} hexagonal crystals, maximum 15 mm large and 5 mm thick. The crystals show a very strong dichroism with cobalt blue and green-yellow colours when observed along [0001] and [1000], respectively. The mineral is transparent, uniaxial (+) and its lustre is vitreous. The hardness is about 6 (Mohs scale), showing a poor {0001} cleavage, irregular to conchoidal fracture, and a measured density of 2.67(8) g cm−3. Laurentthomasite is hexagonal, space group P6/mcc (no. 192), with a=9.95343(6) Å, c=14.15583(8) Å, V=1214.54(1) Å3 and Z=2. The strongest nine lines in the X-ray powder diffraction pattern [d in Å – (I) – hkl] are 3.171 – (10) – 211, 4.064 – (8) – 112, 2.732 – (8) – 204, 4.965 – (6) – 110, 2.732 – (4) – 204, 3.533 – (3) – 004, 7.055 – (2) – 002, 4.302 – (2) – 200 and 3.675 – (2) – 202. Chemical analyses by electron microprobe and several spectroscopies (inductively coupled plasma, ICP; optical emission, OES; mass, MS; and Mössbauer) give the following empirical formula based on 30 anions per formula unit: (Mg0.86 Sc0.54 Fe0.352+ Mn0.26)∑=2.01(K0.89 Na0.05 Y0.02 Ca0.01 Ba0.01)∑=0.98[(Be2.35 Al0.50 Mg0.11 Fe0.033+)∑=2.99(Si11.90 Al0.10)O30]; the simplified formula is (Mg, Sc)2(K, Na)[(Be, Al, Mg)3(Si, Al)12O30]. The crystal structure was refined to an R index of 1.89 % based on 430 reflections with Io > 2σ(I) collected on a four-circle diffractometer with CuKα radiation. By comparison with the general formula of the milarite group, A2B2C[T(2)3T(1)12O30](H2O) x (0

The crystal structure of tlapallite has been determined using single-crystal X-ray diffraction and supported by electron probe micro-analysis, powder diffraction and Raman spectroscopy. Tlapallite is trigonal, space group P321, with a = 9.1219(17) Å, c = 11.9320(9) Å and V = 859.8(3) Å3, and was refined to R_1 = 0.0296 for 786 reflections with I > 2σ(I). This study resulted from the discovery of well-crystallised tlapallite at the Wildcat prospect, Utah, USA. The chemical formula of tlapallite has been revised to (Ca,Pb)_3CaCu_6[Te^(4+)_3Te^(6+)O_(12)]_2(Te^(4+)O_3)_2(SO_4)_2·3H_2O, or more simply (Ca,Pb)_3CaCu_6Te^(4+)_8Te^(6+)_2O_(30)(SO_4)_2·3H_2O, from H_6(Ca,Pb)_2(Cu,Zn)_3(TeO_3)_4(TeO_6)(SO_4). The tlapallite structure consists of layers containing distorted Cu^(2+)O_6 octahedra, Te^(6+)O_6 octahedra and Te^(4+)O_4 disphenoids (which together form the new mixed-valence phyllotellurate anion [Te^(4+)_3Te^(6+)O_(12)]^(12−)), Te^(4+)O_3 trigonal pyramids and CaO_8 polyhedra. SO_4 tetrahedra, Ca(H_2O)_3O_6 polyhedra and H_2O groups fill the space between the layers. Tlapallite is only the second naturally occurring compound containing tellurium in both the 4^+ and 6^+ oxidation states with a known crystal structure, the other being carlfriesite, CaTe^(4+)_2Te^(6+)O_8. Carlfriesite is the predominant secondary tellurium mineral at the Wildcat prospect. We also present an updated structure for carlfriesite, which has been refined to R_1 = 0.0230 for 874 reflections with I > 2σ(I). This updated structural refinement improves upon the one reported previously by refining all atoms anisotropically and presenting models of bond valence and Te^(4+) secondary bonding.

Science et art réunis pour informer, séduire L’exposition Trésors de la Terre, présentée dans l’aile droite de la Galerie de minéralogie et de géologie au Jardin des Plantes de Paris, offre une approche à la fois scientifique et esthétique du monde des minéraux. Les quelque six cents spécimens minéralogiques présentés, allant de cristaux géants aux gemmes de la Couronne de France, reflètent sa diversité, sa complexité et sa richesse artistique. S’appuyant sur des minéraux bruts très variés, s...

The unpublished correspondence between Alfred Des Cloizeaux (1817-1897) and Quintino Sella (1827-1884) is reported and briefly noted. Both of them were students of Henri Hureau de Sénarmont (1808-1862) at the École des Mines (Paris) and their epistolary extends between 1856 and 1884. As well as illustrating the scientific characteristics of the two mineralogists, it offers a panorama of the academic environment of the period in France and in Italy. Political events also transpire, as Sella, after 1860, was committed to building the just unified Italy. The published documents are available in the archives of the Académie des Sciences (Paris) and of the Fondazione Sella (Biella). In particular, Des Cloizeaux pioneered modern microscopy of minerals and promoted the foundation of the Société Française de Minéralogie; Sella introduced new mathematical methods in crystallography and refounded the Accademia dei Lincei., Rivista di Storia dell'Università di Torino, V. 7, N. 1 (2018)

Two new mineral species, trinepheline (NaAlSiO 4 ) and fabriesite (Na 3 Al 3 Si 3 O 12 · 2H 2 O), are described from late-stage metamorphic veins of the jadeite deposit of Tawmaw-Hpakant (Myanmar). Both minerals and their names were approved by the IMA Commission on New Minerals and Mineral Names (IMA 2012–024 and IMA 2012–080). The name trinepheline is known in literature for the polymorphs of synthetic NaAlSiO 4 with a value of the c parameter that is three times that of nepheline. Fabriesite is named in memory of Jacques Fabries (1932–2000), former professor of the “Museum National d’Histoire Naturelle” in Paris (France). Fabriesite and trinepheline occur intimately intergrown together with nepheline, more rarely with albite and other feldspar-group phases such as banalsite and stronalsite; other associated minerals are jadeite and secondary products like natrolite and harmotome. All phases have been identified via electron backscatter diffraction (EBSD) patterns. Both fabriesite and trinepheline are pseudomorph after jadeite and occur as skeletal allotriomorphic crystals up to 15–20 μm long and 5–10 μm wide. They are white to yellowish in hand specimen, colourless in thin section; the streak is white and the lustre appears vitreous to greasy; they are non-fluorescent; Mohs’ hardness is 5–5½. Empirical formulae (EMPA analysis) are very close to the ideal compositions with traces of Ca and K for trinepheline, and of Ca, K, Ba, Mg, Fe, and Mn for fabriesite. Calculated densities are 2.642 g cm −3 for trinepheline (space group P 6 1 , a = 9.995 A, c = 24.797 A) and 2.386 g cm −3 for fabriesite (space group Pna 2 1 , a = 16.426 A, b = 15.014 A, c = 5.223 A), respectively. The strongest five lines in the calculated X-ray powder diffraction patterns [ d (A) ( I )( hkl )] are: 3.163(100)(122), 3.834(81)(023), 4.133(49)(006), 3.272(40)(120) and 2.403(31)(127) for trinepheline; 3.41(100)(240), 4.41(77)(201), 2.97(70)(421), 2.61(40)(002) and 8.21(36)(200) for fabriesite.

Dana Symposium, May 24, 2006, Baltimore, MD, U.S.A.