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

Abstract

Davidbrownite-(NH4), (NH4,K)5(V4+O)2(C2O4)[PO2.75(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)3.11K1.73Na0.09]Σ4.93[(V4+1.92Mg0.01Al0.02)Σ1.95O2](C2O4) [(P3.94As0.12)Σ4.06O10.94(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) Å3 and Z = 2. The crystal structure of davidbrownite-(NH4) (R1 = 0.0524 for 2062 Io > 2σI reflections) consists of a chain structural unit with the formula {(V4+O)2(C2O4)[PO2.75(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.

Thebaite-(NH4), (NH4,K)3Al(C2O4)(PO3OH)2(H2O), a new phosphate–oxalate mineral from the Rowley mine, Arizona, USA

“…These structures take advantage of the oxalate group's ability to form strong bidentate linkages between octahedra. Such strong bidentate linkages between octahedra also occur in the structures of the other two oxalatophosphate minerals, phoxite, (NH 4 ) 2 Mg 2 (C 2 O 4 )(PO 3 OH) 2 (H 2 O) 4 (Kampf et al , 2019a) and davidbrownite-(NH 4 ), (NH 4 ,K) 5 (V 4+ O) 2 (C 2 O 4 )[PO 2.75 (OH) 1.25 ] 4 ⋅3H 2 O (Kampf et al , 2019b), which both are found in the Rowley-mine guano mineral assemblage. The oxalate group in the thebaite-(NH 4 ) structure forms a bidentate linkage to a single AlO 6 octahedron, thereby decorating the double-strand chain rather than strongly linking it to other structural components.…”

“…The new mineral was found in a hot and humid area of the mine (see figure 26 in Wilson, 2020) in an unusual bat-guano-related, post-mining assemblage of phases that include a variety of vanadates, phosphates, oxalates and chlorides, some containing NH 4 + . This secondary mineral assemblage is found growing on baryte-quartz-rich matrix and, besides thebaite-(NH 4 ) includes allantoin (Kampf et al , 2020), ammineite, antipinite, aphthitalite, bassanite, biphosphammite, cerussite, davidbrownite-(NH 4 ) (Kampf et al , 2019a), fluorite, halite, hydroglauberite, mimetite, mottramite, natrosulfatourea (Kampf et al , 2020), perite, phoxite (Kampf et al , 2019b), quartz, rowleyite (Kampf et al , 2017), salammoniac, struvite, thénardite, urea, vanadinite, weddellite, willemite, wulfenite and several other potentially new minerals. Thebaite-(NH 4 ) was found in intimate association with antipinite, vanadinite and at least one other new mineral.…”

“…The still actively forming bat guano assemblage at depth (125 feet) in the Rowley mine near Theba, Arizona has already proven to be a remarkable source of new minerals. Among these are the first minerals that contain both oxalate and phosphate groups: phoxite, (NH 4 ) 2 Mg 2 (C 2 O 4 )(PO 3 OH) 2 (H 2 O) 4 (Kampf et al 2019a) and davidbrownite-(NH 4 ), (NH 4 ,K) 5 (V 4+ O) 2 (C 2 O 4 )[PO 2.75 (OH) 1.25 ] 4 ⋅3H 2 O (Kampf et al 2019b). The new mineral described herein, thebaite-(NH 4 ), is the third known mineral containing both of these anionic groups, and several others are currently under study.…”

Dendoraite-(NH4), a new phosphate–oxalate mineral related to thebaite-(NH4) from the Rowley mine, Arizona, USA

“…The new mineral was found in a hot and humid area of the mine (see figure 26 in Wilson, 2020) in an unusual bat guano-related, post-mining assemblage of phases that include a variety of vanadates, phosphates, oxalates and chlorides, some containing NH 4 + . This secondary mineral assemblage is found growing on baryte–quartz-rich matrix and, besides dendoraite-(NH 4 ), includes allantoin (Kampf et al , 2021c), ammineite, antipinite, aphthitalite, bassanite, biphosphammite, cerussite, davidbrownite-(NH 4 ) (Kampf et al , 2019a), fluorite, halite, hydroglauberite, mimetite, mottramite, natrosulfatourea (Kampf et al , 2021c), perite, phoxite (Kampf et al , 2019b), relianceite-(K) (Kampf et al , 2022), rowleyite (Kampf et al , 2017), salammoniac, struvite, thebaite-(NH 4 ) (Kampf et al , 2021a), thénardite, urea, vanadinite, weddellite, willemite, wulfenite, and several other potentially new minerals. Dendoraite-(NH 4 ) was found in intimate association with antipinite, fluorite, mimetite, mottramite, relianceite-(K), rowleyite, salammoniac, struvite, vanadinite, willemite, wulfenite, and at least one other potentially new species.…”

“…Including the new mineral described herein, dendoraite-(NH 4 ), eight new minerals have now been described from this assemblage. Dendoraite-(NH 4 ), (NH 4 ) 2 NaAl(C 2 O 4 ) (PO 3 OH) 2 (H 2 O) 2 , is one of only five minerals known to include both phosphate and oxalate groups, the others being davidbrownite-(NH 4 ), (NH 4 ,K) 5 (V 4+ O) 2 (C 2 O 4 )[PO 2.75 (OH) 1.25 ] 4 ⋅ 3H 2 O (Kampf et al, 2019a), phoxite, (NH 4 ) 2 Mg 2 (C 2 O 4 ) (PO 3 OH) 2 (H 2 O) 4 (Kampf et al, 2019b), relianceite-(K), K 4 Mg (V 4+ O) 2 (C 2 O 4 )(PO 3 OH) 4 (H 2 O) 10 (Kampf et al, 2022), and thebaite-(NH 4 ), (NH 4 ,K) 3 Al(C 2 O 4 )(PO 3 OH) 2 (H 2 O) (Kampf et al, 2021a); all of these, except phoxite, are known only from the Rowley mine bat guano assemblage. One of these, relianceite-(K), is intimately associated with dendoraite-(NH 4 ) and is described in a companion paper, Kampf et al (2022).…”