Carlsonite, , and huizingite-(Al), (NH4)9Al3(SO4)8(OH)2·4H2O, two new minerals from a natural fire in an oil-bearing shale near Milan, Ohio

The new minerals carlsonite (IMA2014-067), ( NH 4 ) 5 Fe 3 3 + O ( SO 4 ) 6 · 7 H 2 O , and huizingite-(Al) (IMA2015-014), (NH 4 ) 9 Al 3 (SO 4 ) 8 (OH) 2 ·4H 2 O, formed from a natural fire in an oil-bearing shale near Milan, Ohio. Carlsonite crystals are yellow to orange-brown thick tablets, flattened on {001}, or stout prisms, elongated on [110], up to about 0.5 mm in size. The mineral has a tan streak, vitreous luster, Mohs hardness of 2, brittle tenacity, irregular fracture, perfect {001} cleavage, calculated density of 2.167 g/cm 3 , and is easily soluble in H 2 O. Carlsonite is optically biaxial (−), α = 1.576(1), β = 1.585(1), and γ = 1.591(1) (white light). Huizingite-(Al) crystals, typically intergrown in light greenish yellow drusy aggregates, are tabular to bladed, flattened on {100}, up to about 0.25 mm in maximum dimension. The mineral has a white streak, vitreous luster, Mohs hardness of 2½, brittle tenacity, irregular fracture, no cleavage, calculated density of 2.026 g/cm 3 , and is easily soluble in H 2 O. Huizingite-(Al) is optically biaxial (+) with α = 1.543(1), β = 1.545(1), and γ = 1.563(1) (589.6 nm light). Raman and infrared spectroscopy was conducted on both minerals. Electron microprobe analyses provided the empirical formulas [ ( NH 4 ) 4 . 64 Na 0 . 24 K 0 . 12 ] Σ 5 . 00 Fe 3 . 05 3 + O ( SO 4 ) ⋅ 6 . 93 H 2 O and [ ( NH 4 ) 8 . 76 Na 0 . 22 K 0 . 02 ] Σ 9 . 00 ( Al 1 . 65 Fe 1 . 34 3 + ) Σ 2 . 99 ( OH ) 1 . 98 ( H 2 O ) 4 . 02 ( SO 4 ) 8 . 00 for carlsonite and huizingite-(Al), respectively. Huizingite compositions with Fe > Al were noted. Carlsonite is triclinic, P 1 ¯ , a = 9.5927(2), b = 9.7679(3), c = 18.3995(13) A, α = 93.250(7)°, β = 95.258(7)°, γ = 117.993(8)°, V = 1506.15(16) A 3 , and Z = 2. Huizingite-(Al) is triclinic, P 1 ¯ , a = 9.7093(3), b = 10.4341(3), c = 10.7027(8) A, α = 77.231(5)°, β = 74.860(5)°, γ = 66.104(5)°, V = 948.73(9) A 3 , and Z = 1. The five strongest lines in the X-ray powder diffraction pattern of carlsonite are [ d obs in A( I ) ( hkl )]: 9.23(100)(002); 8.26(40)(100,011); 7.57(43)( 1 ¯ 11,1 1 ¯ 1,011); 4.93(23)( 1 ¯ 1 ¯ 1, 1 ¯ 20); and 3.144(41)(multiple). Those for huizingite-(Al) are: 8.82(60)(100); 5.04(69)(121); 3.427(100)( 2 ¯ 2 ¯ 1); 3.204(68)( 2 ¯ 11); and 3.043(94)(2 1 ¯ 2,312). The crystal structures of carlsonite ( R 1 = 0.030) and huizingite ( R 1 = 0.040) are bipartite, each consisting of a structural unit and an interstitial unit. For carlsonite, the structural unit is a [ Fe 3 3 + O ( H 2 O ) 3 ( SO 4 ) 6 ] 5 − cluster and the interstitial complex is [(NH 4 ) 5 (H 2 O) 4 ] 5+ . For huizingite-(Al), the structural unit is a [(Al,Fe 3+ ) 3 (OH) 2 (H 2 O) 4 (SO 4 ) 6 ] 5− cluster and the interstitial complex is [(NH 4 ) 5 (H 2 O) 4 ] 5+ . In the carlsonite cluster, three FeO 6 octahedra share a common vertex, while in the huizingite-(Al) cluster, three (Al,Fe)O 6 octahedra form an abbreviated corner-linked chain. The cluster in carlsonite is the same as that in metavoltine, while the huizingite-(Al) cluster is unique. The range of Lewis basicity of the structural unit in carlsonite is 0.23–0.11 valence units (v.u.) and in huizingite-(Al) it is 0.20–0.12 v.u.; the corresponding Lewis acidities of the interstitial complexes in these structures are 0.13 and 0.14 v.u., respectively. A characteristic Lewis acid strength of 0.13 v.u. is suggested for NH 4 + when it is in its most typical coordinations of 7 to 8. The close structural relationship between carlsonite and metavoltine and the similarity of their powder diffraction patterns suggests that carlsonite may have misidentified as metavoltine in some NH 4 -rich mineral assemblages. The new heteropolyhedral cluster in the structure of huizingite-(Al) is of interest because its existence may provide insights into the structural and paragenetic relations among hydrated ferric sulfate minerals. In particular, it may exist as a complex in aqueous solutions or in solid-state transformations involving the formation and/or breakdown of sideronatrite-style [Fe 3+ (SO 4 ) 3 ] 3− chains. We surmise that it may be a more commonly formed mineral than its abundance would indicate and that its rarity may reflect a narrow stability range, and so a transitory existence.