• journal_title：Mineralogical Magazine
• Contributor：S. J. Mills ; M. S. Rumsey ; G. Favreau ; J. Spratt ; M. Raudsepp ; M. Dini
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2011.075.1.135
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：75
• issue：1
• firstpage：135
• section：Articles

Bariopharmacoalumite, ideally Ba_0.5Al₄(AsO₄)₃(OH)₄·4H₂O, is a new mineral from Cap Garonne, France. It occurs in several places within the mine as colourless to pale yellow interpenetrating cubes up to 0.5 mm across. Bariopharmacoalumite is transparent to translucent, with a white streak, has an adamantine lustre and imperfect cleavage on {001}. The Vickers hardness is 234.35 and the Mohs harness is 3.5. Bariopharmacoalumite is isotropic, with m>nm> = 1.573 (upper estimate) [calculated from reflectance values at 589 nm using Fresnel Equations]. The empirical formula, based on 20 oxygen atoms, is: (Ba_0.54Cu_0.03K_0.01)_Σ0.58(Al_3.99Fe_0.02)_Σ4.01(AsO₄)_3.00(OH)_3.85O_0.15·4H₂O and the calculated density (on the basis of the empirical formula and single-crystal unit cell) is 2.580 g/cm³. The four strongest lines in the X-ray powder diffraction pattern are [m>dm>_obs(Å), m>Im>_obs,(m>hklm>)]: 7.759, 100, (001); 5.485, 27, (011); 3.878, 27, (002); 4.454, 18, (011). Bariopharmacoalumite from Cap Garonne is cubic, space group m>Pm>mg class="inline-graphic" alt="Graphic" src="135/embed/inline-graphic-1.gif" />3m>mm> with m>am> = 7.742(4) Å, m>Vm> = 464.2(4) ų and m>Zm> = 1. The crystal structure was solved by direct methods and refined to m>Rm>₁ = 0.0705 for 215 reflections with m>Im> > 4σ(m>Im>) and is consistent with members of the pharmacosiderite supergroup. Data are also presented from zoned bariopharmacoalumite–bariopharmacosiderite crystals found at the Mina Grande mine, Chile.