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Davidbrownite-(NH₄), (NH₄,K)₅(V⁴⁺O)₂(C₂O₄)[PO_(2.75)(OH)_(1.25)]₄·3H₂O, a new phosphate–oxalate mineral from the Rowley mine, Arizona, USA

Kampf, Anthony R. and Cooper, Mark A. and Rossman, George R. and Nash, Barbara P. and Hawthorne, Frank. C. and Marty, Joe (2019) Davidbrownite-(NH₄), (NH₄,K)₅(V⁴⁺O)₂(C₂O₄)[PO_(2.75)(OH)_(1.25)]₄·3H₂O, a new phosphate–oxalate mineral from the Rowley mine, Arizona, USA. Mineralogical Magazine, 83 (6). pp. 869-877. ISSN 0026-461X. doi:10.1180/mgm.2019.56.

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Davidbrownite-(NH₄), (NH₄,K)₅ (V⁴⁺O)₂(C₂O₄)[PO_(2.75)(OH)_(1.25)]₄·3H₂O, is a new mineral species from the Rowley mine, Maricopa County, Arizona, USA. It occurs in an unusual bat-guano-related, post-mining assemblage of phases that include a variety of vanadates, phosphates, oxalates and chlorides, some containing NH⁴⁺. Other secondary minerals found in association with davidbrownite-(NH₄) are antipinite, fluorite, mimetite, mottramite, quartz, rowleyite, salammoniac, struvite, vanadinite, willemite and wulfenite. Crystals of davidbrownite-(NH4) are light green–blue needles or narrow blades up to ~0.2 mm long. The streak is white, the lustre is vitreous, Mohs hardness is ca. 2, tenacity is brittle and fracture is splintery. There are two good cleavages in the [010] zone, probably {100} and {001}. The measured density is 2.12(2) g cm⁻³. Davidbrownite-(NH₄) is optically biaxial (+) with α = 1.540(2), β = 1.550(5) and γ = 1.582(2) (white light); 2V = 58.5(5)°; moderate r > v dispersion; and orientation Z = b and Y ≈ a. Pleochroism: X = pale blue, Y = nearly colourless, Z = light blue; and Y < X < Z. Electron microprobe analysis gave the empirical formula [(NH₄)_(3.11)K_(1.73)Na_(0.09)]_(Σ4.93)[(V⁴⁺_(1.92)Mg_(0.01)Al_(0.02))_(Σ1.95)O₂](C₂O₄) [(P_(3.94)As_(0.12))_(Σ4.06)O_(10.94)(OH)_(5.06)]·3H₂O, with the C and H content provided by the crystal structure. Raman and infrared spectroscopy confirmed the presence of NH₄ and C₂O₄. Davidbrownite-(NH₄) is monoclinic, P2₁/c, with a = 10.356(6), b = 8.923(5), c = 13.486(7) Å, β = 92.618(9)°, V = 1244.9(12) ų and Z = 2. The crystal structure of davidbrownite-(NH₄) (R₁ = 0.0524 for 2062 I_o > 2σI reflections) consists of a chain structural unit with the formula {(V⁴⁺O)₂(C₂O₄)[PO_(2.75)(OH)_(1.25)]₄}⁵⁻, and a disordered interstitial complex containing five large monovalent cations (NH⁴⁺ and K⁺) and three H₂O groups pfu. Strong hydrogen bonds form links within and between the chains.

Item Type:Article
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URLURL TypeDescription
Kampf, Anthony R.0000-0001-8084-2563
Rossman, George R.0000-0002-4571-6884
Additional Information:© 2019 Mineralogical Society of Great Britain and Ireland. One anonymous reviewer, Igor V. Pekov and Structures Editor Peter Leverett are thanked for constructive comments, which improved the manuscript. Keith Wentz, claim holder of the Rowley mine, is thanked for allowing underground access for the study of the occurrence and the collecting of specimens. This study was funded, in part, by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County, by NSF grant EAR-1322082 to GRR and by a Natural Sciences and Engineering Research Council Discovery Grant and a Canada Foundation for Innovation Grant to FCH.
Funding AgencyGrant Number
John Jago Trelawney EndowmentUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Canada Foundation for InnovationUNSPECIFIED
Subject Keywords:davidbrownite-(NH4), new mineral species, phosphate, oxalate, hydrogen bonding, crystal structure, Rowley mine, Arizona, USA
Issue or Number:6
Record Number:CaltechAUTHORS:20200213-124534342
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Official Citation:Kampf, A., Cooper, M., Rossman, G., Nash, B., Hawthorne, F., & Marty, J. (2019). Davidbrownite-(NH4), (NH4,K)5(V4 O)2(C2O4)[PO2.75(OH)1.25]4·3H2O, a new phosphate–oxalate mineral from the Rowley mine, Arizona, USA. Mineralogical Magazine, 83(6), 869-877. doi:10.1180/mgm.2019.56
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101273
Deposited By: Tony Diaz
Deposited On:13 Feb 2020 21:20
Last Modified:16 Nov 2021 18:01

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