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Bracewellite

Formula:
CrO(OH)
System:OrthorhombicColour:Deep red to black
Hardness:5½ - 6½
Name:For Smith Bracewell, formerly Director, British Guyana Geological Survey, who first noted the occurrence.
Polymorph of:Grimaldiite, Guyanaite


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
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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:
McconnelliteGuyanaiteGrimaldiiteEskolaite

Physical Properties of Bracewellite

Diaphaneity (Transparency):Translucent
Colour:Deep red to black
Streak:Dark brown
Hardness (Mohs):5½ - 6½
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 = 9.86Å, 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:Vary rarely as minute crystals; in crystalline masses; in alluvial grains
X-Ray Powder Diffraction:
d-spacingIntensity
4.065 (vvs)
2.648 (vs)
2.404 (vs)
2.458 (w)
2.149 (w)
3.314 (vw)
Comments:Recorded on type material

Optical Data of Bracewellite

Type:Biaxial

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
         (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 Group:
Diaspore Group:
M
3+
 
O(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,Fe)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
[(OH)
 
2
|TeO
 
4
]
4.FD.30Khinite
Pb
2+
 
Cu
2+
3
(TeO
 
6
)(OH)
 
2
4.FD.30Parakhinite
Pb
2+
 
Cu
2+
3
TeO
 
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(Ti,Cr,Fe,Mg,Zr)
 
21
O
 
38
7.14.7Mcconnellite
CuCrO
 
2
7.14.8Redledgeite
Ba
 
x
([Cr,Fe,V]
3+
2x
Ti
 
8-2x
)O
 
16
7.14.9Hawthorneite
BaMgTi
 
3
Cr
 
4
Fe
 
4
O
 
19
7.14.10Zincochromite
ZnCr
 
2
O
 
4
7.14.11Wattersite
(Hg-Hg)
2+
2
Hg
2+
 
[O
 
2
|CrO
 
4
]
7.14.12Chromite
FeCr
 
2
O
 
4
7.14.13Magnesiochromite
MgCr
 
2
O
 
4
7.14.14 Donathite

Other Names for Bracewellite

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

Other Information

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

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    Localities for Bracewellite

    (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.
    Guyana
     
    • Mazaruni District
      • Kamakusa
    		Geol.Soc.Amer.,Progr.Ann. Meeting (1967) p. 151; MINERALOGICAL MAGAZINE, DECEMBER 1984, VOL. 48, PP. 560 2
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