• journal_title：Mineralogical Magazine
• Contributor：H. Effenberger ; W. Krause ; H.-J. Bernhardt ; M. Martin
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2000-
• Format：text/html
• Language：en
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：64
• issue：6
• firstpage：1109
• section：Articles

Rappoldite, the Co-analogue of helmutwinklerite, and zincgartrellite, the Zn-dominant analogue of gartrellite, are two new members of the tsumcorite group. Both minerals are triclinic, their structures are closely related to the parent structure, i.e. the ‘tsumcorite type’ (C2/m, Z = 2). The lower symmetry is caused by two different crystal-chemical requirements. Order phenomena of the hydrogen bonds cause the ‘helmutwinklerite type’ (P1̅, Z = 4), ordering of Cu<sup>2+sup> and Fe<sup>3+sup> is responsible for the ‘gartrellite type’ (P1̅, Z = 1).

Rappoldite was found on samples from the Rappold mine near Schneeberg, Saxony, Germany. The new species forms red to red-brown prismatic and tabular crystals up to 1 mm long. D<sub>calc.sub> = 5.28 g/cm<sup>3sup>. 2V<sub>zsub> = 85(5)°, n<sub>xsub> = 1.85 (calc.), n<sub>ysub> = 1.87(2) and n<sub>zsub> = 1.90(2); dispersion is distinct with r > v; orientation is Y ~|| [1̅20] and X ~ || c. The empirical formula derived from electron microprobe analyses is (Pb<sub>1.01sub>Ca<sub>0.01sub>)<sub>∑1.02sub>(Co<sub>0.99sub>Ni<sub>0.62sub>Zn<sub>0.35sub>Fe<sub>0.02sub>)<sub>∑1.98sub>[(AsO<sub>4sub>)<sub>1.99sub>(SO<sub>4sub>)<sub>0.01sub>]<sub>∑2.00sub>[(OH)<sub>0.02sub>(H<sub>2sub>O)<sub>1.98sub>]<sub>∑2.00sub> or Pb(Co,Ni)<sub>2sub>(AsO<sub>4sub>)<sub>2sub>·2H<sub>2sub>O. Single-crystal X-ray studies showed average C2/m symmetry. Weak superstructure reflections are responsible for triclinic symmetry and enlarged cell metrics (refined from powder data): a = 11.190(2) Å , b = 10.548(2) Å , c = 7.593(1) Å , α = 100.38(1)°, β = 109.59(2)°, γ = 98.96(1)°, V = 807.6 Å<sup>3sup>, Z = 4. The superstructure results from the hydrogen-bond scheme, but faint streaks indicate some disorder. All investigated rappoldite crystals are twinned by reflection on (23̅0) which corresponds to the mirror plane of the average C2/m cell. Helmutwinklerite is isotypic with rappoldite and probably also with pure thometzekite; sulphatian thometzekite is monoclinic.

Zincgartrellite forms green-yellow rosette-like aggregates on samples from the Tsumeb mine, Namibia. The D<sub>calc.sub> = 5.30 g/cm<sup>3sup>. 2V<sub>xsub> = 87(5)°, n<sub>xsub> = 1.91(2), n<sub>ysub> = 1.94 (calc.) and n<sub>zsub> = 1.97(2). Electron-microprobe analyses and Mössbauer data yielded the empirical formula (Pb<sub>0.97sub>Ca<sub>0.04sub>)<sub>∑1.01sub>(Zn<sub>0.91sub>Cu<sub>0.51sub>Fe<sub>0.59sub>Al<sub>0.03sub>) <sub>∑2.04sub>[(AsO<sub>4sub>)<sub>1.96sub>(SO<sub>4sub>)<sub>0.01sub>] <sub>∑1.97sub>[(OH)<sub>0.81sub>(H<sub>2sub>O)<sub>1.31sub>] <sub>∑2.12sub> or Pb(Zn,Fe,Cu)<sub>2sub>(AsO<sub>4sub>)<sub>2sub>(H<sub>2sub>O,OH)<sub>2sub>. The structural formula is Pb(Zn<sub>xsub>Fe<sub>1−xsub>)(Zn<sub>xsub>Cu<sub>1−xsub>)(AsO<sub>4sub>)<sub>2sub>(OH)<sub>1−xsub> (H<sub>2sub>O)<sub>1+xsub> with 0.4 < x < 0.8. Gartrellite is defined by x < 0.4. Helmutwinklerite has x near to 1 and is defined by a cell with fourfold volume. Single-crystal X-ray studies of zincgartrellite proved space group P1̅ caused by ordering of Fe<sup>3+sup> and Cu at one atomic site. Cell parameters (refined from powder data): a = 5.550(1) Å , b = 5.620(1) Å , c = 7.621(1) Å , α = 68.59(1), β = 69.17(1), γ = 69.51(1)°, V = 200.1 Å <sup>3sup>, Z = 1.