TY - JOUR
T1 - Putnisite, SrCa4Cr
3+ 8 (CO
3)8SO
4(OH)16. 25H
2O, a new mineral from Western Australia
T2 - Description and crystal structure
AU - Elliott, P
AU - Giester, G
AU - Rowe, R
AU - Pring, Allan
PY - 2014
Y1 - 2014
N2 - Putnisite, SrCa4Cr3+ 8 (CO3)8SO4(OH)16.25H 2O, is a new mineral from the Polar Bear peninsula, Southern Lake Cowan, Western Australia, Australia. The mineral forms isolated pseudocubic crystals up to 0.5 mm in size in a matrix composed of quartz and a near amorphous Cr silicate. Putnisite is translucent, with a pink streak and vitreous lustre. It is brittle and shows one excellent and two good cleavages parallel to {100}, {010} and {001}. The fracture is uneven and the Mohs hardness 12. The measured density is 2.20(3) g/cm3 and the calculated density based on the empirical formula is 2.23 g/cm3. Optically, putnisite is biaxial negative, with a = 1.552(3), b = 1.583(3) and g = 1.599(3) (measured in white light). The optical orientation is uncertain and pleochroism is distinct: X pale bluish grey, Y pale purple, Z pale purple. Putnisite is orthorhombic, space group Pnma, with a = 15.351(3), b = 20.421(4) Å , c = 18.270(4) Å , V = 5727(2) Å 3 (single-crystal data), and Z = 4. The strongest five lines in the X-ray powder diffraction pattern are [d(Å)(I)(hkl)]: 13.577 (100) (011), 7.659 (80) (200), 6.667 (43) (211), 5.084 (19) (222, 230), 3.689 (16) (411). Electron microprobe analysis (EMPA) gave (wt.%): Na2O 0.17, MgO 0.08, CaO 10.81, SrO 5.72, BaO 0.12, CuO 0.29, Cr2O3 31.13, SO3 3.95, SiO2 0.08, Cl 0.28, CO2calc 17.94, H2Ocalc 30.30, O=Cl 0.06, total 100.81. The empirical formula, based on O + Cl = 69, is: Cr3+ 8.02Ca3.78Sr1.08Na0.11Cu2+ 0.07Mg0.04Ba0.02[(SO4)0.96(SiO 4)0.03]0.99 (CO3)7.98(OH)16.19Cl0.15.24.84H2O. The crystal structure was determined from single-crystal X-ray diffraction data (MoKa, CCD area detector and refined to R1 = 5.84% for 3181 reflections with F0 > 4sF. Cr(OH)4O2 octahedra link by edge-sharing to form an eight-membered ring. A 10-coordinated Sr2+ cation lies at the centre of each ring. The rings are decorated by CO3 triangles, each of which links by corner-sharing to two Cr(OH)4O2 octahedra. Rings are linked by Ca(H2O)4O4 polyhedra to form a sheet parallel to (100). Adjacent sheets are joined along [100] by corner-sharing SO4 tetrahedra. H2O molecules occupy channels that run along [100] and interstices between slabs. Moderate to weak hydrogen bonding provides additional linkage between slabs.
AB - Putnisite, SrCa4Cr3+ 8 (CO3)8SO4(OH)16.25H 2O, is a new mineral from the Polar Bear peninsula, Southern Lake Cowan, Western Australia, Australia. The mineral forms isolated pseudocubic crystals up to 0.5 mm in size in a matrix composed of quartz and a near amorphous Cr silicate. Putnisite is translucent, with a pink streak and vitreous lustre. It is brittle and shows one excellent and two good cleavages parallel to {100}, {010} and {001}. The fracture is uneven and the Mohs hardness 12. The measured density is 2.20(3) g/cm3 and the calculated density based on the empirical formula is 2.23 g/cm3. Optically, putnisite is biaxial negative, with a = 1.552(3), b = 1.583(3) and g = 1.599(3) (measured in white light). The optical orientation is uncertain and pleochroism is distinct: X pale bluish grey, Y pale purple, Z pale purple. Putnisite is orthorhombic, space group Pnma, with a = 15.351(3), b = 20.421(4) Å , c = 18.270(4) Å , V = 5727(2) Å 3 (single-crystal data), and Z = 4. The strongest five lines in the X-ray powder diffraction pattern are [d(Å)(I)(hkl)]: 13.577 (100) (011), 7.659 (80) (200), 6.667 (43) (211), 5.084 (19) (222, 230), 3.689 (16) (411). Electron microprobe analysis (EMPA) gave (wt.%): Na2O 0.17, MgO 0.08, CaO 10.81, SrO 5.72, BaO 0.12, CuO 0.29, Cr2O3 31.13, SO3 3.95, SiO2 0.08, Cl 0.28, CO2calc 17.94, H2Ocalc 30.30, O=Cl 0.06, total 100.81. The empirical formula, based on O + Cl = 69, is: Cr3+ 8.02Ca3.78Sr1.08Na0.11Cu2+ 0.07Mg0.04Ba0.02[(SO4)0.96(SiO 4)0.03]0.99 (CO3)7.98(OH)16.19Cl0.15.24.84H2O. The crystal structure was determined from single-crystal X-ray diffraction data (MoKa, CCD area detector and refined to R1 = 5.84% for 3181 reflections with F0 > 4sF. Cr(OH)4O2 octahedra link by edge-sharing to form an eight-membered ring. A 10-coordinated Sr2+ cation lies at the centre of each ring. The rings are decorated by CO3 triangles, each of which links by corner-sharing to two Cr(OH)4O2 octahedra. Rings are linked by Ca(H2O)4O4 polyhedra to form a sheet parallel to (100). Adjacent sheets are joined along [100] by corner-sharing SO4 tetrahedra. H2O molecules occupy channels that run along [100] and interstices between slabs. Moderate to weak hydrogen bonding provides additional linkage between slabs.
KW - Crystal structure
KW - New mineral species
KW - Polar Bear peninsula
KW - Putnisite
KW - Strontium calcium chromium sulfate carbonate
KW - Western Australia
UR - http://www.scopus.com/inward/record.url?scp=84899680381&partnerID=8YFLogxK
U2 - 10.1180/minmag.2014.078.1.10
DO - 10.1180/minmag.2014.078.1.10
M3 - Article
VL - 78
SP - 131
EP - 144
JO - Mineralogical Magazine
JF - Mineralogical Magazine
SN - 0026-461X
IS - 1
ER -