Meyrowitzite

Meyrowitzite was discovered underground in the Markey mine, Red Canyon, Suan Juan County, Utah, U.S.A. It has not been found in any other location. Mineralized channels of meyrowitzite are in the Shinarump Member of the Chinle Formation. The Shinarump member is made up of medium-to coarse-grained sandstone, conglomeratic sandstone beds, and thick siltstone lenses. Ore minerals were deposited as replacements of wood and other organic materials and as disseminations in the enclosing sandstone. Since the closing of the Markey mine, oxidation of primary ores in the humid underground environment has produced a variety of secondary minerals. These secondary minerals are primarily sulfates as efflorescent crusts on the surfaces of mine walls. It is found on calcite-veined asphaltum in association with gypsum, markeyite, and rozenite.[1]

Meyrowitzite has bladed crystals with a length up to about 0.2 mm. The blades are commonly irregular and radiating outward from a central point. Blades are elongate on [010], flattened on {100} and exhibit the forms {100}, {001}, {101}, {110}, and {011}. There was no twinning observed. It is a transparent yellow with vitreous luster and a very pale yellow streak. It displays variable fluorescence from weak greenish-yellow to moderate greenish blue under a 405 nm laser. It has a hardness of 2 based on Mohs hardness scale. It has brittle tenacity, irregular fracture, and one perfect cleavage on {-101}. The density was measured at 2.70(2) g*cm^-3 by flotation in a methylene iodide and toluene mixture. It is easily soluble in room temperature water. It is optically biaxial (+) with α = 1.520(2), β = 1.528(2), and γ = 1.561(2) measured in white light. The 2V measured using extinction data analyzed with EXCALIBRW is 53.0(6)°; the calculated 2V is 53.3°. The dispersion is weak, r > v. The optical orientation is Z = b, Y ^ a ≈ 19° in obtuse β. Crystals are weakly pleochroic in shades of pale yellow, X ≈ Y < Z. The Gladstone–Dale compatibility, 1 – (KP/KC) is –0.039 (excellent) using the empirical formula, and –0.035 (excellent) using the ideal formula, where k(UO₃) = 0.134.[2]

Meyrowitzite has a crystal structure based on a unique corrugated uranyl carbonate heteropolyhedral sheet. Meyrowitzite is dimorphous with Zellerite but Zellerites structure is not known. The PXRD patterns for Meyrowitzite and Zellerite are quite different. Although the strongest peaks in the Zellerite pattern are represented in the Meyrowitzite pattern, the four strongest lines in the Meyrowitzite pattern are not in the Zellerite pattern.[1]

There are three U sites in Meyrowitzite's structure. Two (U1 and U2) are surrounded by eight O atoms. This forms a squat UO₈ hexagonal bipyramid. (U3) is surrounded by seven O atoms forming a squat UO₇ pentagonal bipyramid. The two short apical bonds of all three bipyramids constitute the UO₂ 2+ uranyl group. Of the six CO₃ 2– groups in the structure, three centered by C1, C2, and C3 share alternating equatorial edges of the U1 hexagonal bipyramid, thereby forming the well-known uranyl tricarbonate (UTC) unit. The other three, centered by C4, C5, and C6, share alternating equatorial edges of the U2 hexagonal bipyramid, forming a second UTC unit. The five equatorial corners of the U3 pentagonal bipyramid are shared with O atoms of the C1, C2, C3, C4, and C6 carbonate groups. These linkages create a unique corrugated uranyl carbonate heteropolyhedral sheet parallel to {101}. The U2 UTCs are oriented perpendicular to the plane of the sheet with the unshared corner of the C5 carbonate group pointing away from the sheet. Three Ca atoms (Ca1, Ca2, and Ca3) are eightfold-coordinated to O atoms in the sheets and to OW atoms, although Ca3 is effectively only sevenfold-coordinated because two of its ligands (OW15 and OW16) are only half-occupied. The Ca polyhedra do not link to one another; instead, they share edges and corners with the polyhedra in the uranyl carbonate heteropolyhedral sheets, thereby linking the sheets into a framework. The fully occupied OW9 through OW13 sites and the half-occupied OW14 and OW17 sites are located in the cavities in this framework.[1]

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