Klebelsbergite, Sb₄O₄(OH)₂SO₄: redefinition and synthesis

Klebelsbergite is verified as a valid mineral species, in museum specimens from the type locality, Baia Sprie (Felsöbánya), Rumania.

Klebelsbergite occurs as pale yellow to orange-yellow crystals radially grown on stibnite. Wet-chemical analysis of synthetic klebelsbergite, supported by electron microprobe analyses of natural material, gives Sb 71.78, S 4.65, H₂O 2.69, O 20.88% (by difference). The empirical cell contents are Sb_4.07O_5.00(SO₄ · 1.03H₂O with an ideal formula Sb₄O₄(OH)₂SO₄. The crystals are tabular or acicular elongated [001], flattened {010}. The mineral is orthorhombic, Pcmb or Pc2₁b, a = 11.279(2), b = 14.909(3), c = 5.7648(6)A; Z = 4. D(meas) = 4.62(6), D(calc) = 4.69g/cm³. The strongest lines of the X-ray powder pattern are 6.22(s)(120), 3.892(s)(211), 3.545(s)(221), 3.150(s)(301), 3.131(vs)(231), 2.830(s)(012), 2.435(s)(132), 1.805(s)(213). Klebelsbergite has vitreous luster, yellow streak, and no distinct cleavage. The mineral is optically biaxial with large 2V_x about 70°, β ≅ 1.95, and is not pleochroic. VHN = 200 (l0g load).

Single crystals of klebelsbergite were synthesized by boiling 2 g of Sb₂O₃ with 600 ml of 1 N H₂SO₄ for four days. Synthetic crystals are tabular, elongated [001], flattened {010}. The space group, cell parameters, and powder-diffraction data are essentially identical to those of natural klebelsbergite. The crystals decompose by dehydration at 273°C.