Mindat Logo

Bracewellite

This page is currently not sponsored. Click here to sponsor this page.



Formula:
CrO(OH)
System:OrthorhombicColour:Deep red to black
Hardness:5½ - 6½
Member of:Diaspore Group
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.
Polymorph of:Grimaldiite, Guyanaite
Isostructural with: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.
Diaspore Group.

Classification of Bracewellite

IMA status:Approved
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:6.1.1.5

6 : HYDROXIDES AND OXIDES CONTAINING HYDROXYL
1 : XO(OH)
Hey's CIM Ref.:7.14.2

7 : Oxides and Hydroxides
14 : Oxides of Cr
mindat.org URL:http://www.mindat.org/min-748.html
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:
QuartzPyrophylliteMcconnelliteGuyanaiteGrimaldiite
GoldGahniteEskolaite

Physical Properties of Bracewellite

Lustre:Sub-Vitreous, Sub-Metallic
Diaphaneity (Transparency):Translucent, Opaque
Colour:Deep red to black
Streak:Dark brown
Hardness (Mohs):5½ - 6½
Tenacity:Brittle
Cleavage:None Observed
Fracture:Irregular/Uneven
Density (measured):4.45 - 4.48 g/cm3
Density (calculated):4.28 g/cm3

Crystallography of Bracewellite

Crystal System:Orthorhombic
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 ų (Calculated from Unit Cell)
Z:4
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:
d-spacingIntensity
4.901 (vvw)
4.065 (vvs)
3.314 (vw)
2.648 (vs)
2.546 (vw)
2.548 (w)
2.404 (vs)
2.458 (w)
2.209 (vw)
2.149 (w)
1.678 (wb)
(
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

Type:Biaxial
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

Formula:
CrO(OH)
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:

- +
Diaspore
AlO(OH)
Goethite
α-Fe
3+
 
O(OH)
Groutite
Mn
3+
 
O(OH)
Montroseite
(V
3+
 
,Fe
3+
 
)O(OH)
Tsumgallite
GaO(OH)
Related Minerals - Nickel-Strunz Grouping):

- +
4.FD.05Spertiniite
Cu(OH)
 
2
4.FD.10Diaspore
AlO(OH)
4.FD.10Goethite
α-Fe
3+
 
O(OH)
4.FD.10Groutite
Mn
3+
 
O(OH)
4.FD.10Guyanaite
CrO(OH)
4.FD.10Montroseite
(V
3+
 
,Fe
3+
 
)O(OH)
4.FD.10Tsumgallite
GaO(OH)
4.FD.15Manganite
Mn
3+
 
O(OH)
4.FD.20Yttrotungstite-(Y)
YW
 
2
O
 
6
(OH)
 
3
4.FD.20Yttrotungstite-(Ce)
(Ce,Nd,Y)W
 
2
O
 
6
(OH)
 
3
4.FD.20Unnamed (Nd-analogue of Yttrotungstite-(Ce))
(Nd,Ce,La)W
 
2
O
 
6
(OH)
 
3
4.FD.25Frankhawthorneite
Cu
 
2
Te
6+
 
O
 
4
(OH)
 
2
4.FD.30Khinite
Pb
2+
 
Cu
2+
3
Te
6+
 
O
 
6
(OH)
 
2
4.FD.30Parakhinite
Pb
2+
 
Cu
2+
3
Te
6+
 
O
 
6
(OH)
 
2
Related Minerals - Hey's Index Grouping:

- +
7.14.1Eskolaite
Cr
 
2
O
 
3
7.14.3Grimaldiite
CrO(OH)
7.14.4Guyanaite
CrO(OH)
7.14.5Yimengite
K(Cr,Ti,Fe,Mg)
 
12
O
 
19
7.14.6Mathiasite
(K, Ba, Sr)(Zr, Fe)(Mg,Fe)
 
2
(Ti,Cr,Fe)
 
18
O
 
38
7.14.7Mcconnellite
CuCrO
 
2
7.14.8Redledgeite
Ba(Ti
4+
6
Cr
3+
2
)O
 
16
7.14.9Hawthorneite
Ba(MgTi
 
3
Cr
 
4
Fe
 
4
)O
 
19
7.14.10Zincochromite
ZnCr
 
2
O
 
4
7.14.11Wattersite
(Hg
+
2
)
 
2
Hg
2+
 
(CrO
 
4
)O
 
2
7.14.12Chromite
Fe
2+
 
Cr
3+
2
O
 
4
7.14.13Magnesiochromite
Mg(Cr,Al,Fe)
 
2
O
 
4

Other Names for Bracewellite

Synonyms:
IMA1967-035
Other Languages:
German:Bracewellit
Russian:Брацевеллит
Spanish:Bracewellita

Other Information

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

Reference List:

- +
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

Search Engines:
  • Look for Bracewellite on Google
  • Look for Bracewellite images on Google
  • External Links:
  • Look for Bracewellite on Webmineral
  • Look for Bracewellite on Athena Mineralogy
  • Look for Bracewellite on Mineralien Atlas
  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Bracewellite details from Handbook of Mineralogy (PDF)
  • Mineral Dealers:
  • Buy RARE Minerals from Rocks of Africa
  • Fine Minerals from Weinrich Minerals, Inc.
  • Lapis Mineral Magazin
  • rare and unusual minerals mainly crystallized
  • Search for Bracewellite on Well-Arranged Molecules
  • Top quality minerals from Kristalle of California
  • Bracewellite specimens for sale - minfind.com
  • Rare and Unusual minerals at Mineralogical Research Company
  • The Arkenstone - Fine Minerals
  • Buy from McDougall Minerals
  • High-end worldwide specimens & outstanding customer service
  • Fine minerals from bisbeeborn.com
  • 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.
    Australia
     
    • South Australia
      • Eyre Peninsula
        • Middleback Range
          • Iron Knob
    Minerals of Iron Monarch, Glyn L. Francis
    Guyana
     
    • Mazaruni District
      • Kamakusa
    Geol.Soc.Amer.,Progr.Ann. Meeting (1967) p. 151; MINERALOGICAL MAGAZINE, DECEMBER 1984, VOL. 48, PP. 560 2
    Mineral and/or Locality  
    Search Google  
    Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
    Current server date and time: October 13, 2014 01:57:39
    Mineral and Locality Search
    Mineral:
    and/or Locality:
    Options
    Fade toolbar when not in focusFix toolbar to bottom of page
    Hide Social Media Links
    Slideshow frame delay seconds