Publication Date:
2013-10-26
Description:
The new mineral leverettite (IMA 2013-011), ideally Cu 3 CoCl 2 (OH) 6 , was found at the Torrecillas mine, Salar Grande, Iquique Province, Chile, where it occurs as a supergene alteration phase in association with akaganéite, anhydrite, chalcophanite, goethite, halite, manganite, pyrite, quartz and todorokite. Crystals of leverettite are steep rhombohedra to 1 mm with {101} prominent and modified by {001}, sometimes forming V-shaped twins by reflection on {102I}. The crystals can also form finger-like, parallel stacked growths along the c axis. The new mineral is medium to deep green in colour and has a light green streak. Crystals are transparent with a vitreous lustre. Mohs hardness is ~3 and the crystals have a brittle tenacity, a perfect cleavage on {101} and a conchoidal fracture. The measured density is 3.64(2) g cm –3 and calculated density based on the empirical formula is 3.709 g cm –3 . Optically, leverettite is uniaxial (–) with and 〉 1.8 and exhibits pleochroism with O (bluish green) 〉 E (slightly yellowish green). The empirical formula, determined from electron-microprobe analyses is Cu 3 (Co 0.43 Cu 0.40 Mn 0.17 Ni 0.07 Mg 0.01 ) 1.08 Cl 1.87 O 6.13 H 6 . Leverettite is trigonal (hexagonal), space group R 3I m , unit-cell parameters a = 6.8436(6) and c = 14.064(1) Å, V = 570.42(8) Å 3 , Z = 3. The eight strongest X-ray powder diffraction lines are [ d obs Å( I )( hkl )]: 5.469(90)(101), 4.701(18)(003), 2.905(22)(021), 2.766(100)(113), 2.269(66)(024), 1.822(26)(033), 1.711(33)(220), 1.383(23)(128). The structure, refined to R 1 = 0.023 for 183 F o 〉 4 F reflections, shows leverettite to be isostructural with herbertsmithite and gillardite.
Print ISSN:
0026-461X
Electronic ISSN:
1471-8022
Topics:
Geosciences
Permalink