Contribution
Santanait, ein neues Bleichromat-Mineral
[Santanaite, a new lead chromate mineral]
Mücke, Arno
Neues Jahrbuch für Mineralogie - Monatshefte Jg. 1972 Heft 10 (1972), p. 455 - 457
2 références bibliographiques
publié: Dec 22, 1972
DOI: 10.1127/njmm/1972/1972/455
ArtNo. ESP156197210003, Prix: 19.00 €
Abstract
The mineral occurs at Mina Santa Ana, Caracoles, Sierra Gorda, Chile in a druse surrounded by strongly corroded galena and closely associated with phoenicochroite, also with chromatian wulfenite, quartz, diaboleite, and an unknown triclinic chromate mineral. Electron microprobe analysis gave Pb 88.O, Cr 1.9, O (by difference) 10.1 %, corresponding very closely to Pb11CrO16. Santanaite is hexagonal, space group D66 — P6322, a0 = 9.03 Å ± 0.01, c0 = 39.84 ± 0.08. The mineral occurs as aggregates of straw-yellow platelets, up to 0.5 mm long, 0.2 mm wide. Luster adamantine, Cleavages {0001} perfect, also {1210}, rarely {1010}. H about 4. Optical uniaxial, negative, nα = 2.12, nᵧ = 2.32 (S-Se melts). The mineral polished well, shows dirthy gray-brown colours, and weak reflection pleochroism. Reflectance about 15 % therefore less than that of phoenicochroite. Under crossed Nicols the anisotropy effects are not recognizable because of the whitish-yellow to yellow internal reflections.
Mots-clefs
Santanaite • lattice constants • space group • optical properties; Chile