| Reference Type | Journal (article/letter/editorial) |
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| Title | Bicapite, KNa2Mg2(H2PV5+14O42)·25H2O, a new polyoxometalate mineral with a bicapped Keggin anion from the Pickett Corral mine, Montrose County, Colorado, U.S.A. |
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| Journal | American Mineralogist |
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| Authors | Kampf, Anthony R. | Author |
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| Hughes, John M. | Author |
| Nash, Barbara P. | Author |
| Marty, Joe | Author |
| Year | 2019 (December 1) | Volume | 104 |
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| Page(s) | 1851-1856 | Issue | 12 |
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| Publisher | Mineralogical Society of America |
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| Download URL | https://rruff.info/rruff_1.0/uploads/AM104_1851.pdf+ |
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| DOI | doi:10.2138/am-2019-7027Search in ResearchGate |
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| Classification | Not set | LoC | Not set |
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| Mindat Ref. ID | 398734 | Long-form Identifier | mindat:1:5:398734:0 |
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| GUID | 8284ad36-9c76-4967-ab81-ea68d47ff4f4 |
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| Full Reference | Kampf, Anthony R., Hughes, John M., Nash, Barbara P., Marty, Joe (2019) Bicapite, KNa2Mg2(H2PV5+14O42)·25H2O, a new polyoxometalate mineral with a bicapped Keggin anion from the Pickett Corral mine, Montrose County, Colorado, U.S.A. American Mineralogist, 104 (12) 1851-1856 doi:10.2138/am-2019-7027 |
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| Plain Text | Kampf, Anthony R., Hughes, John M., Nash, Barbara P., Marty, Joe (2019) Bicapite, KNa2Mg2(H2PV5+14O42)·25H2O, a new polyoxometalate mineral with a bicapped Keggin anion from the Pickett Corral mine, Montrose County, Colorado, U.S.A. American Mineralogist, 104 (12) 1851-1856 doi:10.2138/am-2019-7027 |
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| In | (2019, December) American Mineralogist Vol. 104 (12) Mineralogical Society of America |
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| Abstract/Notes | Bicapite, KNa2Mg2(H2PV145+O42)·25H2O, is a new mineral species (IMA2018-048) discovered at the Pickett Corral mine, Montrose County, Colorado, U.S.A. Bicapite occurs as square tablets up to about 0.2 mm on edge on montroseite-corvusite-bearing sandstone. Crystals are dark red-brown, often appearing black. The streak is orange, and the luster is vitreous. Bicapite is brittle, has a Mohs hardness of 1½, and displays one excellent cleavage on {100}. The measured density is 2.44(2) g/cm3. Bicapite is uniaxial (+), ω = 1.785(5), ε ≈ 1.81 (white light); pleochroism is red-brown; E > O, slight. The electron probe microanalysis and results of the crystal structure determination provided the empirical formula (based on 67 O apfu) (K1.23Na2.23Mg1.48)Σ4.94[H2.51P1.02(V13.915+Mo0.076+)Σ13.98O42]·25H2O. Bicapite is tetragonal, I4/m, with a = 11.5446(12) Å, c = 20.5460(14) Å, V = 2738.3(6) Å3, and Z = 2. The strongest four lines in the diffraction pattern are [d in Å (I) (hkl)]: 10.14 (100) (002,101); 2.978 (29) (134,206); 2.809 (11) (305); and 2.583 (11) (420,008). The atomic arrangement of bicapite was solved and refined to R1 = 0.0465 for 1008 independent reflections with I > 2σI. The structural unit is a [H2PV125+O40(V5+O)2]7– heteropolyanion composed of 12 distorted VO6 octahedra surrounding a central PO4 tetrahedron and capped on opposite sides by two VO5 square pyramids; the structural unit is a modification of the α-isomer of the Keggin anion, [XM12O40]n–. Charge balance in the structure is maintained by the [KNa2Mg2(H2O)25]7+ interstitial complex. The name bicapite is in recognition of this being the only known mineral with a structure based on a bicapped Keggin anion. The discovery of bicapite and numerous other natural polyoxometalate compounds in the Colorado Plateau uranium/vanadium deposits make that the most productive region found to date for naturally occurring polyoxometalate compounds. |
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