Rakovanite
Rakovanite, Na3{H3[V10O28]}•15H20, is a member of the pascoite family. It is a transparent, brittle mineral occurring in the monoclinic crystal system. It is orange in color and has an orange-yellow colored streak. Rakovanite is soft with a Mohs hardness of 1 and a calculated density of 2.407g cm−3. It does not fluoresce in long- or short-wave ultraviolet radiation. Rakovanite crystals are up to one mm in maximum dimension and vary in habit from blocky to prismatic on [001], commonly exhibiting steps and striations parallel to [001]. Its name honors John Rakovan, professor, Department of Geology and Environmental Earth Science, Miami University, Oxford, Ohio, US.[2]
| Rakovanite | |
|---|---|
 Well formed rakovanite crystals from the type locality: Sunday Mine, Slick Rock Mining District, San Miguel County, Colorado. | |
| General | |
| Category | Pascoite family |
| Formula (repeating unit) | Na3{H3[V10O28]}•15H2O |
| Strunz classification | 8.CJ.45 |
| Dana classification | 40.4.7.4 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/n |
| Unit cell | a = 12.0248(17), b = 17.121(3), c = 18.140(3) Å, β 106.242(8)°; Z = 4 |
| Identification | |
| Color | Orange |
| Crystal habit | Blocky to prismatic on [100] |
| Fracture | Conchodial |
| Tenacity | Brittle |
| Mohs scale hardness | 1 |
| Luster | Subadamantine |
| Streak | Orange-yellow |
| Diaphaneity | Transparent |
| Specific gravity | 2.407 (calculated) |
| Optical properties | Biaxial (+) |
| Refractive index | α589nm = 1.776(5) β589nm = 1.803(5) γ589nm = 1.910(6) |
| Birefringence | δ = 0.134 |
| Pleochroism | X light yellow, Y orangish yellow, Z yellowish orange, Z > Y> X |
| 2V angle | 2Vz540nm =58(1); 2Vz589nm = 56(1); 2Vz650nm =53(1)° |
| Dispersion | r < v, strong parallel |
| Other characteristics | Surface relief: very high Orientation: X + b; Z Λ c= 8° in obtuse β It does not fluorescence in long- or short-wave ultraviolent radiation. |
| References | [1][2] |
Occurrence
Rakovanite was found on specimens from the Sunday mine and the West Sunday mine, Slick Rock district, San Miguel County, Colorado, US.[2]
It occurs as crystalline crusts on sandstone fractures in the mine walls of the Sunday and West Sunday mines. The best crystals were found perched on an amorphous dehydrated vanadium phase along with crystals tightly adhered to a corvusite-montroseite matrix.[2]
It forms from the oxidation of montroseite-corvusite assemblages. It is associated calcite, corvusite, hewettite, hughesite, montroseite, munirite, paramontroseite, pascoite, rossite, sherwoodite, and other unidentified vanadium phases as well as at least two other potentially new decavanadate species. It forms aqueous solutions of relatively low pH when water reacts with pyrite in the deposit under ambient temperatures and generally oxidizing near-surface environments.[2]
Atomic arrangement
Rakovanite crystal unit consists of the decavanadate polyanion similar to that found in other decavanadate-bearing mineral. The decavanadate polyanion is formed of ten distorted, edge-sharing octahedra which differs in rakovanite unlike other minerals. It contains three hydrogen atoms, forming a {H3[V10O28]}3- anionic complex. Its individual polyanions are linked to an interstitial complex.[2]
Chemical composition
| Oxide | wt% | Normalized wt% | Ideal |
|---|---|---|---|
| Na2O | 8.02 (0.40) | 6.90 | 7.15 |
| K2O | 0.29 (0.05) | 0.25 | - |
| MgO | 0.01 (0.01) | 0.01 | - |
| CaO | 0.04 (0.02) | 0.03 | - |
| V2O5 | 81.2 (1.1) | 69.90 | 69.97 |
| Al2O3 | 0.04 (0.04) | 0.03 | - |
| H2O | 22.87 | 22.87 | |
| Total | 100.00 |
Empirical formula (based on V = 10 apfu): (Na2.90K0.07Ca0.01Al0.01)ε2.99{H2.98[V10O28]}•15H2O; the ideal formula is Na3{H3[V10O28]}•15H2O calculated as ideal value for Na3{H3[V10O28]}•15H2O. Composition normalized to 100% using ideal H2O value from crystal structure results.[2]
See also
- Classification of minerals
- List of minerals
References
- "Rakovanite: Rakovanite mineral information and data". www.mindat.org. Retrieved 2015-12-01.
- Kampf, A. R.; Hughes, J. M.; Marty, J.; Gunter, M. E.; Nash, B. (2011). "Rakovanite, Na3V10O28•15H2O, A New Member of the Pascoite Family with a Protonated Decavanadate Polyanion". The Canadian Mineralogist. 49 (2): 595–604. doi:10.3749/canmin.49.2.595.