Abstract

The new mineral parascholzite, CaZn2(PO4)2 · 2H2O, from Hagendorf, Bavaria, is monoclinic, Cc or C2/c, with a = 17.864(5), b = 7.422(2), c = 6.674(2)Å, and β = 106°27(1)′. Comparison with scholzite from Reaphook Hill, South Australia shows that the two minerals are dimorphous, scholzite being orthorhombic, Pbc21, with a = 17.178(8), b = 22.24(1), and c = 6.681(3)Å. Aside from its monoclinic distortion, the unit cell of parascholzite corresponds to the subcell of scholzite, which has B = b/3 = 7.413Å and symmetry Pbcn. Both scholzite and parascholzite are derived from this basic structure. Weak diffuse nonrational superstructure reflections from parascholzite indicate a supercell with c′ ≈ 3c. Parascholzite is invariably twinned with {100} as both the twin and composition plane.

Parascholzite is white to colorless with a white streak. The specific gravity is 3.12 (obs.) and density 3.10 g/cm3 (calc.). Hardness (Mohs) is 4. Optically it is biaxial (+) with 2Vz =25° (obs.), r > v, α = 1.587, β = 1.588, γ = 1.603; the orientation of the indicatrix is b||X and cΛZ = 13° in the acute angle between c and a.

Physical, optical, and morphological properties of the two minerals are similar, but parascholzite may be distinguished by its inclined extinction and unique powder diffraction lines at 4.158 and 2.779Å. Scholzite and parascholzite commonly form syntaxial intergrowths with (100) the composition plane. Much previously published scholzite data were obtained from these intergrowths or from parascholzite itself, which explains some of the confusion in the literature on the former mineral. A new set of physical, optical and crystallographic data for Australian scholzite is presented. Worldwide occurrences of the two minerals are also reviewed.

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