Markascherite, Cu-3(M0O4)(OH)(4), a new mineral species polymorphic with szenicsite, from Copper Creek, Pinal County, Arizona, U.S.A.

作者：Yang H^*; Jenkins R A; Thompson R M; Downs R T; Evans S H; Bloch E M

来源：American Mineralogist, 2012, 97(1): 197-202.

DOI：10.2138/am.2012.3895

• Markascherite
• szenicsite
• molybdate
• copper oxysalt
• crystal structure
• X-ray diffraction
• Raman spectra

A new mineral species, markascherite (IMA2010-051), ideally Cu-3(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 [10 (1) over bar]. The mineral is green, transparent with green streak and vitreous luster. It is brittle and has a Mohs hardness of 3.5 similar to 4; cleavage is perfect on {100} and no parting was observed. The calculated density is 4.216 g/cm(3). Optically, markascherite is biaxial (-), with n(alpha) >1.8, n(beta)> 1.8, and n gamma >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 Cu-2.89(Mo1.04O4)(OH)(4).
Markascherite, polymorphic with szenicsite, is monoclinic, with space group P2(1)/nt and unit-cell parameters a = 9.9904(6), b = 5.9934(4), c = 5.5255(4) angstrom, beta = 97.428(4)degrees, and V= 328.04(4) angstrom(3). 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, Cu-4(DO2)(M0O(4))(2)(OH)(6), given the coupled substitution of [2Cu(2+) + 2(OH-)](2+) for [(U6+ square) + 2O(2)](2+). The Raman spectra of markascherite are compared with those of two other copper molybdate minerals szenicsite and lindgrenite.

• 出版日期2012-1