Original paper

Gilmarite, Cu3 (AsO4) (OH)3, a new mineral: its description and crystal structure

Sarp, Haul; Černý, Radovan

European Journal of Mineralogy Volume 11 Number 3 (1999), p. 549 - 556

19 references

published: May 25, 1999
manuscript accepted: Jan 6, 1999
manuscript received: Mar 6, 1998

DOI: 10.1127/ejm/11/3/0549

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ArtNo. ESP147051103013, Price: 29.00 €

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Abstract

Abstract Gilmarite, CU3 (AsO4) (OH)3, occurs at the old copper mines of Roua (Alpes-Maritimes, France), associated with cuprite, posnjackite, langite, clinotyrolite, connellite, brochantite, malachite, vesignieite, cornubite, olivenite, trippkeite, domeykite and djurleite. It forms rosettes (0.3 mm diameter) or isolated crystals (0.1 × 0.04x0.02 mm maximum dimension). The green-blue crystals are elongated along [101] or [100], flattened on {010} and have a good cleavage on {010}. They are not twinned. The mineral is triclinic, P 1, a = 5.445 (4), b = 5.873 (3), c = 5.104 (3) Å, α = 114.95 (3), β = 93.05 (5), γ = 91.92 (4)°, V = 147.5 (2) Å3, Z = 1, Dmeas = 4.2 (1) and Dcalc = 4.28 g/cm3.The strongest lines in the X-ray powder diffraction pattern (dobs in Å, (hk1), lvis) are: 4.613, (001), 100; 4.580, (011̅), 50; 3.390, (101), 60; 2.713, (200), 40; 2.543, (01̅̅̅̅̅2̄) (12̄1̄), 40. Mohs’ hardness is ~3. Luster is vitreous transparent, streak is bluish green; crystals are biaxial (-) with α = 1.760 (5), β = 1.80 (1), γ = 1.83 (1) at 589 nm; 2 Vobs = 77 (4)°, 2 Vcalc = 80 (1)°. Pleochroism is weak with γ= green;, α , β = light green. The crystal structure was solved by direct methods (MoKα radiation) and refined using 1640 observed unique reflections to R = 0.062, Rw = 0.041. Gilmarite is a polymorph of clinoclase, their structures are quite different. The structure of gilmarite is formed by infinite chains of CuO6 octahedra and CuO5 square pyramids extending along the b axis. These chains are connected via CuO5 square pyramids to form sheets parallel to (001). The sheets are connected via AsO4 tetrahedra.

Keywords

gilmaritenew mineralpowder patterncrystal structurearsenatecopperhydrogen bonding