• journal_title：The Canadian Mineralogist
• Contributor：Anthony R. Kampf ; John M. Hughes ; Joe Marty ; Barbara Nash
• Publisher：Mineralogical Association of Canada
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.49.5.1243
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：49
• issue：5
• firstpage：1243
• section：Articles

Gunterite, Na₄(H₂O)₁₆(H₂V₁₀O₂₈)·6H₂O, is a new mineral species from the West Sunday mine, Slick Rock district, San Miguel County, Colorado, U.S.A. Crystals of gunterite are tabular on {001} and generally stacked into elongate curved multiple crystals up to 0.5 mm in maximum dimension; the crystals are orange-yellow, with a yellow streak. The mineral displays a subadamantine luster, and is transparent; it does not fluoresce in short- or long-range ultraviolet radiation. Gunterite has a hardness of about 1, a brittle tenacity, and an irregular fracture; no cleavage or parting was observed. The density calculated from the empirical formula using the single-crystal cell data is 2.398 g cm⁻³. Gunterite is biaxial (+), with α 1.735(5), β 1.770(5) and γ 1.825(5); 2V is equal to 78° (white light). The dispersion v < r is strong and parallel. Optical orientation; X = b, Y ≈ c; pleochroism: X yellow, Y orange, Z yellow; Y > X > Z. Gunterite is soluble in water at room temperature. Electronprobe microanalysis and the crystal-structure solution provided the empirical formula (V + Al = 10 apfu): (Na_3.20K_0.02Ca_0.87)_∑4.09[H_1.06(V_9.99Al_0.01)_∑10O₂₈]·22H₂O. The simplified formula of gunterite is Na₄(H₂O)₁₆(H₂V₁₀O₂₈)·6H₂O. There is extensive substitution of Ca for Na in gunterite, yielding a structural formula of (Na_4−xCa_x)_∑4.00(H₂O)₁₆(H_2−xV₁₀O₂₈)·6H₂O; the average value of x from the chemical analyses is 0.85. Gunterite is monoclinic, C2/m, with a 19.848(2), b 10.1889(11), c 13.1184(15) Å, β 130.187(9)°, V 2026.6(4) ų, and Z = 2. The strongest four lines in the diffraction pattern [d in Å(I)hkl] are: 10.01(100)2̄01,001, 8.44(72)110, 8.09(46)1̄11, and 2.997(29)3̄31,401. The atomic arrangement of gunterite was refined to R₁ = 0.0632. The structural unit is a doubly-protonated decavanadate polyanion, {H₂[V₁₀O₂₈]}. The interstitial units linking the structural units contain two Na polyhedra; the Na2 polyhedron is split into two partially occupied sites that are 0.76 Å apart, and significant Ca occupies that site. Several of the H₂O molecules in the interstitial complex are disordered. The mineral is named in honor of Mickey E. Gunter, Professor of Mineralogy at the University of Idaho.