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Okayamalite
A valid IMA mineral species
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About Okayamalite
Flag of Okayama Prefecture, Japan
Formula:
Ca2B[BSiO7]
Colour:
cream white
Lustre:
Earthy
Hardness:
5½
Specific Gravity:
3.30 (Calculated)
Crystal System:
Tetragonal
Member of:
Name:
Named after Okayama Prefecture, Japan, which includes the type locality.
This page provides mineralogical data about Okayamalite.
Unique Identifiers
Mindat ID:
7202
Long-form identifier:
mindat:1:1:7202:7
IMA Classification of Okayamalite
Approved
IMA Formula:
Ca2B2SiO7
Approval year:
1997
First published:
1998
Classification of Okayamalite
9.BB.10
9 : SILICATES (Germanates)
B : Sorosilicates
B : Si2O7 groups, without non-tetrahedral anions; cations in tetrahedral [4] and greater coordination
9 : SILICATES (Germanates)
B : Sorosilicates
B : Si2O7 groups, without non-tetrahedral 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 |
|---|---|---|
| Oky | 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 Okayamalite
Earthy
Transparency:
Translucent
Colour:
Cream white
Streak:
White
Hardness:
5½ on Mohs scale
Cleavage:
None Observed
Density:
3.30 g/cm3 (Calculated)
Optical Data of Okayamalite
Type:
Uniaxial (-)
RI values:
nω = 1.700 nε = 1.696
Max. Birefringence:
δ = 0.004
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.
Chemistry of Okayamalite
Mindat Formula:
Ca2B[BSiO7]
Element Weights:
Elements listed:
Crystallography of Okayamalite
Crystal System:
Tetragonal
Class (H-M):
42m - Scalenohedral
Space Group:
P421m
Cell Parameters:
a = 7.1248(2) Å, c = 4.8177(2) Å
Ratio:
a:c = 1 : 0.676
Unit Cell V:
244.56 ų (Calculated from Unit Cell)
Z:
2
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
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Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Display Options
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2D | Stereo | Red-Blue | Red-Cyan
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View
CIF File Best | x | y | z | a | b | c
CIF File Best | x | y | z | a | b | c
Rotation
Stop | Start
Stop | Start
Labels
Console Off | On | Grey | Yellow
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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) |
|---|---|---|---|---|---|---|---|
| 0002589 | Okayamalite | Giuli G, Bindi L, Bonazzi P (2000) Rietveld refinement of okayamalite, Ca2SiB2O7: Structural evidence for the B/Si ordered distribution American Mineralogist 85 1512-1515 |  | 2000 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 2.654 Å | (100) |
| 2.862 Å | (55) |
| 3.479 Å | (40) |
| 1.920 Å | (35) |
| 1.644 Å | (29) |
| 2.129 Å | (20) |
| 1.644 Å | (20) |
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 Okayamalite
General Appearance of Type Material:
grains to 10 μm in equigranular aggregates
Place of Conservation of Type Material:
National Science Museum, Tokyo, under the registered number NSM M-27525.
Associated Minerals at Type Locality:
Synonyms of Okayamalite
Other Language Names for Okayamalite
Relationship of Okayamalite to other Species
Member of:
Other Members of Melilite Group:
| Åkermanite | Ca2Mg[Si2O7] | Tet. 42m : P421m |
| Alumoåkermanite | (CaNa)Al[Si2O7] | Tet. 42m : P421m |
| Bennesherite | Ba2Fe2+[Si2O7] | Tet. 42m : P421m |
| 'Ferri-gehlenite' | Ca2Fe3+[AlSiO7] | |
| Ferroåkermanite | Ca2Fe[Si2O7] | Tet. 42m : P421m |
| Gehlenite | Ca2Al[AlSiO7] | Tet. 42m : P421m |
| Gugiaite | Ca2Be[Si2O7] | Tet. 42m : P42m |
| Hardystonite | Ca2Zn[Si2O7] | Tet. 42m : P421m |
| Hydroxylgugiaite | (Ca,◻)2(Si,Be)[(Be,Si)2O5.5(OH)1.5] | Tet. 42m : P421m |
Related Minerals - Strunz-mindat Grouping
| 9.BB.10 | Hardystonite | Ca2Zn[Si2O7] |
| 9.BB.10 | Jeffreyite | (Ca,Na)2(Be,Al)(Si2O7,HSi2O7) |
| 9.BB.10 | Alumoåkermanite | (CaNa)Al[Si2O7] |
| 9.BB.10 | Åkermanite | Ca2Mg[Si2O7] |
| 9.BB.10 | 'Ferri-gehlenite' | Ca2Fe3+[AlSiO7] |
| 9.BB.10 | Gehlenite | Ca2Al[AlSiO7] |
| 9.BB.10 | Ferroåkermanite | Ca2Fe[Si2O7] |
| 9.BB.10 | Cebollite | Ca5Al2(SiO4)3(OH)4 |
| 9.BB.10 | Hydroxylgugiaite | (Ca,◻)2(Si,Be)[(Be,Si)2O5.5(OH)1.5] |
| 9.BB.10 | Gugiaite | Ca2Be[Si2O7] |
| 9.BB.15 | Barylite | Be2Ba(Si2O7) |
| 9.BB.15 | 'Barylite-1O' | Be2Ba(Si2O7) |
| 9.BB.20 | Bennesherite | Ba2Fe2+[Si2O7] |
| 9.BB.20 | Andrémeyerite | BaFe2+2(Si2O7) |
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 Okayamalite
mindat.org URL:
https://www.mindat.org/min-7202.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Okayamalite
Reference List:
Matsubara, Satoshi, Miyawaki, Ritsuro, Kato, Akira, Yokoyama, Kazumi, Okamoto, Akiyoshi (1998) Okayamalite, Ca2B2SiO7, a new mineral, boron analogue of gehlenite. Mineralogical Magazine, 62 (5) 703-706 doi:10.1180/002646198547936
Olmi, F., Viti, C., Bindi, L., Bonazzi, P., Menchetti, S. (2000) Second occurrence of okayamalite, Ca2SiB2O7: chemical and TEM characterization. American Mineralogist, 85 (10) 1508-1511 doi:10.2138/am-2000-1022
Localities for Okayamalite
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.
Japan (TL) | |
| Matsubara et al. (1998) |
Norway | |
| Olmi et al. (2000) +1 other reference |
Quick NavTopAbout OkayamaliteUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesRelationshipsStrunz-MindatOther InformationInternet Links References Localities Locality List
Fuka mine, Fuka, Bitchū, Takahashi City, Okayama Prefecture, Japan