• journal_title：The Canadian Mineralogist
• Contributor：Hexiong Yang ; Robert A. Jenkins ; Robert T. Downs ; Stanley H. Evans ; Kimberly T. Tait
• Publisher：Mineralogical Association of Canada
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.49.3.877
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：49
• issue：3
• firstpage：877
• section：Articles

A new mineral species, rruffite, ideally Ca₂Cu(AsO₄)₂·2H₂O, has been found in the oxidation zone of the Cu–As orebody in the Maria Catalina mine, Tierra Amarilla, Chile. It is a secondary mineral and occurs in granular or blocky aggregates and druses. Associated minerals include quartz, barite, mansfieldite, alumopharmacosiderite, conichalcite, metazeunerite, and barahonite-(Al). Rruffite is pale or light blue, transparent with white streak and vitreous luster. It is brittle, has a Mohs hardness of ~3 and a perfect cleavage on {010}, and is twinned on (100). The measured and calculated densities are 3.79(3) and 3.77(2) g/cm³, respectively. Rruffite is insoluble in water, acetone, and hydrochloric acid. Optically, it is biaxial (−), with α 1.725(1), β 1.734(1), γ 1.740(1), 2V_meas 80(2)°, Y = b, X ∧ c 49°, and it does not fluoresce under long- or short-wave ultraviolet light. The dispersion is weak, with r < v. An electron-microprobe analysis yielded the empirical formula Ca_2.01Cu_1.01(AsO₄)_2.02·1.9H₂O. Rruffite, isostructural with roselite, is monoclinic, with space group P2₁/c and unit-cell parameters a 5.8618 (2), b 12.7854 (5), c 5.7025 (2) Å, β 109.425(2)°, and V 403.05(3) ų. Its structure is characterized by isolated CuO₄(H₂O)₂ octahedra that are linked by corner-sharing with AsO₄ tetrahedra to form the kröhnkite-type chains parallel to the c axis. These chains are linked together by large Ca cations and hydrogen bonding. Owing to the strong Jahn–Teller effect, the MO₄(H₂O)₂ octahedron in rruffite is the most distorted of all known roselite-group minerals (M = Cu, Co, Mn, Mg, and Zn) in terms of the quadratic elongation of the octahedra. The Raman spectra of rruffite resemble those of arsenate minerals of the roselite group.