Publication details
Smamite, Ca2Sb(OH)(4)[H(AsO4)(2)]center dot 6H(2)O, a new mineral and a possible sink for Sb during weathering of fahlore
| Authors | |
|---|---|
| Year of publication | 2020 |
| Type | Article in Periodical |
| Magazine / Source | American Mineralogist |
| MU Faculty or unit | |
| Citation | |
| Web | https://doi.org/10.2138/am-2020-7133 |
| Doi | http://dx.doi.org/10.2138/am-2020-7133 |
| Keywords | Smamite; new mineral species; arsenate; crystal structure; weathering; fahlore; Sainte-Marie-aux-Mines |
| Description | Smamite, Ca2Sb(OH)(4)[H(AsO4)(2)]center dot 6H(2)O, is a new mineral species from the Giftgrube mine, Rauenthal, Sainte-Marie-Aux-Mines ore-district, Haut-Rhin department, France. It is a supergene mineral found in quartz-carbonate gangue with disseminated to massive tennantite-tetrahedrite series minerals, native arsenic, Ni-Co arsenides, and supergene minerals picropharmacolite, fluckite, and pharmacolite. Smamite occurs as lenticular crystals growing in aggregates up to 0.5 mm across. The new mineral is whitish to colorless, transparent with vitreous luster and white streak; non-fluorescent under UV radiation. The Mohs hardness is3(1/2); the tenacity is brittle, the fracture is curved, and there is no apparent cleavage. The measured density is 2.72(3) g/cm(3); the calculated density is 2.709 g/cm(3) for the ideal formula. The mineral is insoluble in H2O and quickly soluble in dilute (10%) HCl at room temperature. Optically, smamite is biaxial (-), alpha = 1.556(1), beta = 1.581(1), gamma = 1.588(1) (white light). The 2V (meas) = 54(1)degrees; 2V (calc) = 55.1 degrees. The dispersion is weak, r > gamma. Smamite is non-pleochroic. Electron microprobe analyses provided the empirical formula Ca-2 center dot 03Sb(0.97)(OH)(4)[H-1.10(As1.99Si0.01O4)(2)]center dot 6H2O. Smamite is triclinic, P (1) over bar, alpha = 5.8207(4), b = 8.0959(6), c = 8.21296(6) angstrom, alpha = 95.8343(7)degrees, beta = 110.762(8)degrees, gamma = 104.012(7)degrees, V = 402.57(5) angstrom 3, and Z = 1. The structure (Robs = 0.027 for 1518 I>3sI reflections) is based upon {Ca-2(H2O)(6)Sb(OH)(4)[H(AsO4)(2)]} infinite chains consisting of edge-sharing dimers of Ca(H2O)(3)O-2(OH)(2) polyhedra that share edges with Sb(OH)(4)O-2 octahedra; adjacent chains are linked by H-bonds, including one strong, symmetrical H-bond with an O-H bond-length of similar to 1.23 angstrom. The name smamite is based on the acronym of the Sainte-Marie-aux-Mines district. |