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. (3rd December 2019)

• Record Type: Journal Article
• Authors: Kampf, Anthony R.; Cooper, Mark A.; Rossman, George R.; Nash, Barbara P.; Hawthorne, Frank. C.; Marty, Joe
• Is Part Of: Mineralogical magazine. Volume 83:Number 6(2019)
• Page Start: 869
• Page End: 877
• Publication Date: 2019-12-03
• Subjects: davidbrownite-(NH4), -- new mineral species, -- phosphate, -- oxalate, -- hydrogen bonding, -- crystal structure, -- Rowley mine, -- Arizona, USA; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/mgm.2019.56
• Languages: English
• ISSNs: 0026-461X

Abstract

Abstract: Davidbrownite-(NH4 ), (NH4, K)5 (V 4+ O)2 (C2 O4 )[PO2.75 (OH)1.25 ]4 ·3H2 O, 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 K1.73 Na0.09 ]Σ4.93 [(V 4+ 1.92 Mg0.01 Al0.02 )Σ1.95 O2 ](C2 O4 ) [(P3.94 As0.12 )Σ4.06 O10.94 (OH)5.06 ]·3H2 O, with the C and H content provided by the crystal structure. Raman and infrared spectroscopy confirmed the presence of NH4 and C2 O4 . Davidbrownite-(NH4 ) is monoclinic, P 21 / c, with a = 10.356(6), b = 8.923(5), c = 13.486(7) Å, β = 92.618(9)°, V = 1244.9(12) Å 3 and Z = 2. The crystal structure of davidbrownite-(NH4 ) ( R 1 = 0.0524 for 2062 I o > 2σ I reflections) consists of a chain structural unit with the formula {(V 4+ O)2 (C2 O4 )[PO2.75 (OH)1.25 ]4 } 5–, and a disordered interstitial complex containing five large monovalent cations (NH4 + and K + ) and three H2 O groups pfu. Strong hydrogen bonds form links within and between the chains.