Decrespignyite-(Y), a new copper yttrium rare earth carbonate chloride hydrate from Paratoo, South Australia

Authors: Wallwork K.; Kolitsch U.; Pring A.; Nasdala L.

Source: Mineralogical Magazine, Volume 66, Number 1, 1 February 2002 , pp. 181-188(8)

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Abstract:

Decrespignyite-(Y) is a new copper yttrium rare earth carbonate chloride hydrate from the Paratoo copper mine, near Yunta, Olary district, South Australia. Decrespignyite-(Y) occurs as blue crusts, coatings and fillings in thin fissures on the slatey country rock. Individual pseudohexagonal platelets are typically 10–50 µm in maximum dimension and are often curved. Associated minerals include caysichite-(Y), donnayite-(Y), malachite and kamphaugite-(Y). Electron microprobe and CHN analyses gave: Y₂O₃ 42.2; La₂O₃ 0 1; Pr₂O₃ 0.1; Nd₂O₃ 1.3; Sm₂O₃ 1.0; Gd₂O₃ 4; Tb₂O₃ 0.4; Dy₂O₃ 3.7; Ho₂O₃ 2.6; Er₂O₃ 2.5; CaO 0.5; CuO 10.9; Cl 3.0; CO₂ 19.8; H₂O 10.8, yielding an empirical formula of (Y_{3. 08}Gd_{0. 22}Dy_{0. 16}Ho_{0. 11}Er_{0. 10}Nd_{0. 06}Sm_{0. 05}Tb_{0. 02}La_{0. 02}Pr_{0. 01}Ca_0.08)_3.91Cu_1.12(CO₃)_3.70-Cl_0.7(OH)_5.79·2.4H₂O. The simplified formula is (Y,REE)₄Cu(CO₃)₄Cl(OH)₅·2H₂O. The mineral is royal blue to turquoise-blue in colour, transparent, with a pearly to vitreous lustre and a pale blue streak. No cleavage was observed but the morphology suggests that cleavage would be on [010]. The Mohs' hardness is estimated to be 4. The strongest lines in the X-ray powder pattern are {d_obs (I_obs) (hkl)} 22.79 (30) (010); 7.463 (30) (001); 7.086 (50) (011); 6.241 (100) (021); 4.216 (30) (l¯12); 3.530 (40) (022); 3.336 (30) (032); 2.143 (30) (222, 4¯01). The powder diffraction pattern was indexed on a monoclinic cell with a = 8.899(6), b = 22.77(2), c = 8.589(6) Å, beta

= 120.06(5)°, V = 1506.3(7) Å³ and Z = 4. The structure of the new mineral could not be determined but powder diffraction data indicate the space group is P2, Pm or P2/m. The measured density is 3.64(2) g/cm³ and the calculated density is 3.645 g/cm³. Decrespignyite-(Y) is biaxial negative with alpha

= 1.604(4) and gamma

= 1.638(3) with beta

very close to gamma

; pleochroism is medium strong; X very pale bluish, Y and Z bluish (with greenish tint). Decrespignyite-(Y) is a supergene mineral which precipitated from mildly basic carbonated ground waters. The mineral is named after Robert Champion de Crespigny, a prominent figure in the Australian mining industry and chancellor of the University of Adelaide.

Keywords: DECRESPIGNYITE-(Y); NEW MINERAL; RARE EARTH CARBONATES; PARATOO DEPOSIT; SOUTH AUSTRALIA

Language: English

Document Type: Research article

Publication date: 2002-02-01

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