This page is currently not sponsored. Click here to sponsor this page.
|System:||Orthorhombic||Colour:||Deep red to black|
|Hardness:||5½ - 6½|
|Name:||Named in 1967 by Charles Milton, Daniel E. Appleman, Edward Ching-Te Chao, Frank Cuttita, Joseph I. Dinnin, Edward J. Dwornik, Margaret Hall, Blanche L. Ingram, and Harry J. Rose, Jr. in honor of Smith Bracewell [active as a geological author at least in the time period 1927-1962], formerly Director, British Guyana Geological Survey and professor at the University of the West Indies, who first noted the occurrence of merumite, which proved to be eskolaite with a mixture of chromium minerals, including the mineral subsequently named for him.|
|Diaspore, Goethite, Groutite, Montroseite|
Minute prismatic crystals in vugs or intergrown in the groundmass of eskolaite masses. As with other Cr mineral species from the Merume River locality, such as grimaldiite, guyanaite, and mcconnellite, this species is not universally present in every specimen and verification of each specimen is required.
Classification of Bracewellite
|Strunz 8th edition ID:||4/F.07-50|
|Nickel-Strunz 10th (pending) edition ID:||4.FD.10|
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
F : Hydroxides (without V or U)
D : Hydroxides with OH, without H2O; chains of edge-sharing octahedra
|Dana 8th edition ID:||18.104.22.168|
6 : HYDROXIDES AND OXIDES CONTAINING HYDROXYL
1 : XO(OH)
|Hey's CIM Ref.:||7.14.2|
7 : Oxides and Hydroxides
14 : Oxides of Cr
Please feel free to link to this page.
Type Occurrence of Bracewellite
|Type Locality:||Merume river, Kamakusa, Mazaruni District, Guyana|
|Place of Conservation of Type Material:||The Natural History Museum, London, England (No. 1979,136)|
|Year of Discovery:||1967|
|Geological Setting of type material:||In an alluvial placer deposit, in fine-grained intergrowth with other chromium oxide-hydroxide minerals|
|Associated Minerals at type locality:|
Physical Properties of Bracewellite
|Diaphaneity (Transparency):||Translucent, Opaque|
|Colour:||Deep red to black|
|Hardness (Mohs):||5½ - 6½|
|Density (measured):||4.45 - 4.48 g/cm3|
|Density (calculated):||4.28 g/cm3|
Crystallography of Bracewellite
|Class (H-M):||mmm (2/m 2/m 2/m) - Dipyramidal|
|Cell Parameters:||a = 4.492Å, b = 9.860Å, c = 2.974Å|
|Ratio:||a:b:c = 0.456 : 1 : 0.302|
|Unit Cell Volume:||V 131.72 Å³ (Calculated from Unit Cell)|
|Morphology:||Very rarely as "minute deep red to black prismatic crystals [60-200 microns in size] of bracewellite line microscopic fissures and vugs in merumite". bracewellite is not present in all alluvial grains of merumite and, when present, has been found to constitute negligible amounts and in rare cases, up to a dominant part, of a merumite grain.|
|Comment:||Space Group originally given is Pbnm|
|X-Ray Powder Diffraction:|
|Comments:||Recorded on type material. Eskolaite was prominent in the purest sample that could be found and lines attributable to impurities were subtracted from the data set.|
Optical Data of Bracewellite
|Comments:||RI is not reported for this species as the refractive indices are probably very high, and more impostantly, the mineral is very dark, approaching opaque. No reflected light studies are known.|
Chemical Properties of Bracewellite
|Essential elements:||Cr, H, O|
|All elements listed in formula:||Cr, H, O|
|Analytical Data:||(1) Chemical analysis of type material, estimated to contain about 30 wt.-% of eskolaite|
(2) Theoretical values
Electron microprobe analysis (Milton, 1967) indicated that bracewellite varied from 1-12% in Fe2O3 and 2-5% Al2O3.
(1) (2) TiO2 (0.17) Al2O3 (6.2) Fe2O3 (15.1) Cr2O3 (70.6) (89.40) V2O3 (0.64) H2O (6.9) (10.60) sum 99.6 100.00 wt.-%
Relationship of Bracewellite to other Species
|Member of:||Diaspore Group|
|Other Members of Group:|
|Related Minerals - Nickel-Strunz Grouping):|
|Related Minerals - Hey's Index Grouping:|
Other Names for Bracewellite
|Fluorescence in UV light:||Not fluorescent in UV|
|Health Warning:||No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.|
References for Bracewellite
Milton, C., Appleman, D. E., Appleman, M. H., Chao, E. C. T., Cuttitta, F., Dinnin, J. I., Dwornik, E. J., Ingram, B. L. and Rose, H. J., Jr. (1976): Merumite, a complex assemblage of chromium minerals from Guyana. U.S. Geol. Surv. Prof. Paper 887, 1-29. - American Mineralogist (1977), 62, 593 (abstract).
Anthony, J. W. et al. (1997): Handbook of Mineralogy, Vol. 3, 75.
Internet Links for Bracewellite
Localities for Bracewellite
The map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
(TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.