Protocaseyite, a new decavanadate mineral containing a [Al (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 12) ] (super 6+) linear tetramer, a novel isopolycation
Protocaseyite, a new decavanadate mineral containing a [Al (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 12) ] (super 6+) linear tetramer, a novel isopolycation
American Mineralogist (June 2022) 107 (6): 1181-1189
- chemical composition
- color
- Colorado
- crystal form
- crystal structure
- electron probe data
- formula
- hydroxides
- lattice parameters
- new minerals
- optical properties
- oxides
- San Miguel County Colorado
- space groups
- United States
- vanadates
- X-ray diffraction data
- Burro Mine
- polyoxocation
- decavanadate
- Slick Rock mining district
- polyoxometalate
- protocaseyite
- polyoxoanion
Protocaseyite, [Al (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 12) ][V (sub 10) O (sub 28) ].8H (sub 2) O, is a new mineral (IMA2020-090) occurring in low-temperature, post-mining, secondary mineral assemblages at the Burro mine, Slick Rock district, San Miguel County, Colorado, U.S.A. Crystals of protocaseyite are saffron-yellow, thick blades, with pale orange-yellow streak, vitreous luster, brittle tenacity, curved fracture, two very good cleavages, a Mohs hardness of 2, and a density of 2.45(2) g/cm (super 3) . The optical properties of protocaseyite could be only partly determined: biaxial with alpha =1.755(5), beta <1.80, gamma >1.80 (white light); pleochroic with X and Y yellow, Z orange (X nearly equal Y<Z). Electron-probe microanalysis and crystal-structure solution and refinement provided the empirical formula [(Al (sub 3.89) Mg (sub 0.11) Ca (sub 0.02) ) (sub Sigma 4.02) (OH) (sub 6) (H (sub 2) O) (sub 12) ] [H (sub 0.06) V (sub 10) O (sub 28) ].8H (sub 2) O. Protocaseyite is triclinic, P1, a=9.435(2), b=10.742(3), c=11.205(3) Aa, alpha =75.395(7), beta =71.057(10), gamma =81.286(6) degrees , V=1036.4(5) Aa3, and Z=1. The crystal structure (R (sub 1) =0.026 for 4032 I (sub o) >2 sigma I reflections) contains both the [V (sub 10) O (sub 28) ] (super 6-) decavanadate polyoxoanion and a novel [Al (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 12) ] (super 6+) polyoxocation.
