| Abstrakt: |
A new mineral species, markascherite (IMA2010-051), ideally Cu3(MoO4)(OH) 4, has been found at Copper Creek, Pinal County, Arizona, U.S.A. The mineral is of secondary origin and is associated with brochantite, antlerite, lindgrenite, wulfenite, natrojarosite, and chalcanthite. Markascherite crystals are bladed (elongated along the b axis), up to 0.50 x 0.10 x 0.05 mm. The dominant forms are {001}, {100}, and {010}. Twinning is found with the twofold twin axis along [10̅1]. The mineral is green, transparent with green streak and vitreous luster. It is brittle and has a Mohs hardness of 3.5~4; cleavage is perfect on {100} and no parting was observed. The calculated density is 4.216 g/cm³. Optically, markascherite is biaxial (-), with nα > 1.8, nβ > 1.8, and nγ > 1.8. The dispersion is strong (r > v). It is insoluble in water, acetone, or hydrochloric acid. An electron microprobe analysis yielded an empirical formula Cu2.89 (Mo1.04O4 (OH)4. Markascherite, polymorphic with szenicsite, is monoclinic, with space group P21/m and unit-cell parameters a = 9.9904(6), b = 5.9934(4), c = 5.5255(4) Å, β = 97.428(4)°, and V = 328.04(4) ų. Its structure is composed of three nonequivalent, markedly distorted Cu2+(O,OH)6 octahedra and one MoO4 tetrahedron. The Cu1 and Cu2 octahedra share edges to form brucite-type layers parallel to (100), whereas the Cu3 octahedra share edges with one another to form rutile-type chains parallel to the b axis. These layers and chains alternate along [100] and are interlinked together by both MoO4 tetrahedra and hydrogen bonds. Topologically, the structure of markascherite exhibits a remarkable resemblance to that of deloryite, Cu4(UO2)(MoO4)2(OH)6, given the coupled substitution of [2Cu2+ + 2(OH-)]2+ for [(U6+ + □) + 2O2-]2+. The Raman spectra of markascherite are compared with those of two other copper molybdate minerals szenicsite and lindgrenite. [ABSTRACT FROM AUTHOR] |
