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About BracewelliteHide

Deep red to black
Sub-Vitreous, Sub-Metallic
5½ - 6½
Specific Gravity:
4.45 - 4.48
Crystal System:
Member of:
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.
Polymorph of:
Isostructural with:
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.
Diaspore Group.

Classification of BracewelliteHide

First published:

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

1 : XO(OH)

7 : Oxides and Hydroxides
14 : Oxides of Cr

Physical Properties of BracewelliteHide

Sub-Vitreous, Sub-Metallic
Translucent, Opaque
Deep red to black
Dark brown
5½ - 6½ on Mohs scale
None Observed
4.45 - 4.48 g/cm3 (Measured)    4.28 g/cm3 (Calculated)

Optical Data of BracewelliteHide

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 BracewelliteHide


Crystallography of BracewelliteHide

Crystal System:
Class (H-M):
mmm (2/m 2/m 2/m) - Dipyramidal
Cell Parameters:
a = 4.492 Å, b = 9.860 Å, c = 2.974 Å
a:b:c = 0.456 : 1 : 0.302
Unit Cell V:
131.72 ų (Calculated from Unit Cell)
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.
Space Group originally given is Pbnm

X-Ray Powder DiffractionHide

Powder Diffraction Data:
4.901 Å(vvw)
4.065 Å(vvs)
3.314 Å(vw)
2.648 Å(vs)
2.546 Å(vw)
2.548 Å(w)
2.404 Å(vs)
2.458 Å(w)
2.209 Å(vw)
2.149 Å(w)
1.678 Å(wb)
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.

Type Occurrence of BracewelliteHide

Place of Conservation of Type Material:
The Natural History Museum, London, England (No. 1979,136)
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:
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. Geological Survey Proffesional Paper 887: 1-29.

Synonyms of BracewelliteHide

Other Language Names for BracewelliteHide

Relationship of Bracewellite to other SpeciesHide

Member of:
Other Members of this group:
DiasporeAlO(OH)Orth. mmm (2/m 2/m 2/m)
Goethiteα-Fe3+O(OH)Orth. mmm (2/m 2/m 2/m)
GroutiteMn3+O(OH)Orth. mmm (2/m 2/m 2/m) : Pnma

Common AssociatesHide

Associated Minerals Based on Photo Data:
1 photo of Bracewellite associated with GuyanaiteCrO(OH)
1 photo of Bracewellite associated with GrimaldiiteCrO(OH)

Related Minerals - Nickel-Strunz GroupingHide

4.FD.10DiasporeAlO(OH)Orth. mmm (2/m 2/m 2/m)
4.FD.10GroutiteMn3+O(OH)Orth. mmm (2/m 2/m 2/m) : Pnma
4.FD.10GuyanaiteCrO(OH)Orth. mmm (2/m 2/m 2/m)
4.FD.15ManganiteMn3+O(OH)Mon. 2/m : P21/b
4.FD.20Yttrotungstite-(Y)YW2O6(OH)3Mon. 2/m : P21/m
4.FD.20Yttrotungstite-(Ce)(Ce,Nd,Y)W2O6(OH)3Mon. 2 : P21
4.FD.20Unnamed (Nd-analogue of Yttrotungstite-(Ce))(Nd,Ce,La)W2O6(OH)3
4.FD.30KhinitePb2+Cu2+3[Te6+O6](OH)2Orth. mm2 : Fdd2
4.FD.30Khinite-3TPb2+Cu2+3Te6+O6(OH)2Trig. 3 : P32

Related Minerals - Dana Grouping (8th Ed.)Hide mmm (2/m 2/m 2/m)α-Fe3+O(OH)Orth. mmm (2/m 2/m 2/m) mmm (2/m 2/m 2/m) : Pnma,Fe3+)O(OH)Orth.

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

7.14.4GuyanaiteCrO(OH)Orth. mmm (2/m 2/m 2/m)
7.14.6Mathiasite(K, Ba, Sr)(Zr, Fe)(Mg,Fe)2 (Ti,Cr,Fe)18O38Trig.
7.14.9HawthorneiteBaMgTi3Cr4Fe2+2Fe3+2O19Hex. 6/mmm (6/m 2/m 2/m) : P63/mmc
7.14.11Wattersite[Hg2]2+2Hg2+[CrO4]O2Mon. 2/m : B2/b
7.14.12ChromiteFe2+Cr3+2O4Iso. m3m (4/m 3 2/m) : Fd3m
7.14.13MagnesiochromiteMgCr2O4Iso. m3m (4/m 3 2/m) : Fd3m

Fluorescence of BracewelliteHide

Not fluorescent in UV

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for BracewelliteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
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. Geological Survey Professional Paper 887: 1-29.
Fleischer, M., Cabri, L.J., Nickel, E.H., Pabst, A. (1977) New mineral names. American Mineralogist: 62: 593-600.
Anthony, J.W., et al. (1997) Handbook of Mineralogy, Vol. 3: 75.

Internet Links for BracewelliteHide

Localities for BracewelliteHide

This 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.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
  • South Australia
    • Eyre Peninsula
      • Middleback Range
        • Iron Knob
Minerals of Iron Monarch, Glyn L. Francis
Guyana (TL)
  • Potaro-Siparuni Region
    • Kamakusa
Geol.Soc.Amer.,Progr.Ann. Meeting (1967) p. 151. Livingston, A., Jackson, B., Davidson, P.J. (1984) Grimaldiite, CrOOH, a second occurrence, from the Hiaca Mine, Colquechaca, Bolivia. Mineralogical Magazine, 48, 560-562.
Mineral and/or Locality  
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