Fencooperite
A valid IMA mineral species
This page kindly sponsored by Ted Hadley
About Fencooperite
Fen Cooper
Formula:
Ba6Fe3+3Si8O23(CO3)2Cl3 · H2O
Colour:
Jet black to a dirty grey-brown (on very thin edges)
Lustre:
Adamantine, Vitreous
Hardness:
4½ - 5
Specific Gravity:
4.212 (Calculated)
Crystal System:
Trigonal
Name:
Named for California mineral collector Joseph Fenimore Cooper, Jr. (April 30, 1937, Santa Cruz, California - June 6, 2017, Santa Cruz, California). He was an avid collector of western U.S. minerals, especially in California and Nevada, and contributed to more than twenty publications.
This page provides mineralogical data about Fencooperite.
Unique Identifiers
Mindat ID:
10343
Long-form identifier:
mindat:1:1:10343:7
IMA Classification of Fencooperite
Classification of Fencooperite
9.BH.20
9 : SILICATES (Germanates)
B : Sorosilicates
H : Sorosilicates with Si3O10, Si4O11, etc. anions; cations in tetrahedral [4] and greater coordination
9 : SILICATES (Germanates)
B : Sorosilicates
H : Sorosilicates with Si3O10, Si4O11, etc. anions; cations in tetrahedral [4] and greater coordination
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Fco | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Fencooperite
Adamantine, Vitreous
Colour:
Jet black to a dirty grey-brown (on very thin edges)
Streak:
Greyish black
Hardness:
4½ - 5 on Mohs scale
Hardness:
VHN10=269 - 367 kg/mm2 - Vickers
Cleavage:
None Observed
Fracture:
Irregular/Uneven, Sub-Conchoidal
Density:
4.212 g/cm3 (Calculated)
Comment:
Dcalc 4.212 (empirical formula) and 4.338 (ideal formula). Density could not be measured due to small grain size and lack of pure material.
Optical Data of Fencooperite
Type:
Uniaxial (-)
RI values:
nω = 1.723 nε = 1.711
Max. Birefringence:
δ = 0.012
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Very High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized uniaxial interference figure - the conoscopic
(convergent-light, Bertrand-lens-in) view, for a grain cut with the optic axis
centred and vertical. The coloured rings are isochromatics, computed with the
same physics as the Michel-Lévy bar above; the dark cross is the isogyre.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
Pleochroism:
Strong
Comments:
Very strongly pleochroic.
nω = deep bluish-black
nε = light greenish-gray
nω = deep bluish-black
nε = light greenish-gray
Comments:
Absorption: O>>E.
Chemistry of Fencooperite
Mindat Formula:
Ba6Fe3+3Si8O23(CO3)2Cl3 · H2O
Element Weights:
Crystallography of Fencooperite
Crystal System:
Trigonal
Class (H-M):
3m - Ditrigonal Pyramidal
Space Group:
P3m1
Cell Parameters:
a = 10.727 Å, c = 7.085 Å
Ratio:
a:c = 1 : 0.66
Unit Cell V:
706.1 ų
Morphology:
No crystal forms observed.
Twinning:
No twinning observed.
Crystal Structure
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2x2x2 | 3x3x3 | 4x4x4
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0005724 | Fencooperite | Grice J D (2001) The crystal structure of fencooperite: Unique [Fe3O13] pinwheels cross-connected by [Si8O22] islands The Canadian Mineralogist 39 1065-1071 |  | 2001 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 3.892 Å | (100) |
| 3.148 Å | (40) |
| 2.820 Å | (90) |
| 2.685 Å | (80) |
| 2.208 Å | (40) |
| 2.136 Å | (40) |
| 1.705 Å | (35) |
Comments:
Trumbull Peak, California, USA. Data from the type description.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 23 : Subaerial aqueous alteration by non-redox-sensitive fluids (see also #47) |
Type Occurrence of Fencooperite
General Appearance of Type Material:
A dominant phase within black aggregates 2 mm across in barium-silicate-rich lenses. Individual grains are anhedral to somewhat rounded to occasionally platy, and do not exceed 100 µm in size.
Place of Conservation of Type Material:
National Mineral Collection at the Geological Survey of Canada, Ottawa, Ontario, Canada.
Associated Minerals at Type Locality:
Synonyms of Fencooperite
Other Language Names for Fencooperite
Dutch:Fencooperiet
German:Fencooperit
Russian:Фенкуперит
Simplified Chinese:氯碳硅铁钡石
Spanish:Fencooperita
Traditional Chinese:氯碳矽鐵鋇石
Common Associates
Associations Based on Photo Data:
| 5 photos of Fencooperite associated with Sanbornite | BaSi2O5 |
| 3 photos of Fencooperite associated with Gillespite | BaFe2+Si4O10 |
Related Minerals - Strunz-mindat Grouping
| 9.BH. | Bunnoite | Mn2+6AlSi6O18(OH)3 |
| 9.BH.05 | Aminoffite | Ca3(BeOH)2Si3O10 |
| 9.BH.10 | Kinoite | Ca2Cu2(H2O)2[Si3O10] |
| 9.BH.15 | Akatoreite | Mn2+9Al2Si8O24(OH)8 |
Fluorescence of Fencooperite
Not fluorescent.
Other Information
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for Fencooperite
mindat.org URL:
https://www.mindat.org/min-10343.html
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Please feel free to link to this page.
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References for Fencooperite
Localities for Fencooperite
Showing 2 localities.
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and 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).
All localities listed without proper references should be considered as questionable.
USA | |
| Walstrom (n.d.) +2 other references |
| Roberts et al. (2001) +1 other reference |
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Trumbull Peak Ba-silicate deposit, Trumbull Peak, Clearing House, Clearing House Mining District, East Belt, Mariposa County, California, USA