Pentahydroborite
A valid IMA mineral species
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About Pentahydroborite
Formula:
CaB2O(OH)6 · 2H2O
Colour:
Colourless
Lustre:
Vitreous
Hardness:
2½
Specific Gravity:
2.00 - 2.03
Crystal System:
Triclinic
Name:
The "penta" in pentahydroborite is rather a misnomer for a species with only 2 waters, but this came about because the 6 (OH) had originally been mistaken for 3 extra waters.
This page provides mineralogical data about Pentahydroborite.
Unique Identifiers
Mindat ID:
3154
Long-form identifier:
mindat:1:1:3154:3
IMA Classification of Pentahydroborite
Approved
IMA Formula:
CaB2O(OH)6(H2O)·H2O
First published:
1961
Classification of Pentahydroborite
6.BB.10
6 : BORATES
B : Diborates
B : Neso-diborates with double tetrahedra B2O(OH)6; 2(2T)
6 : BORATES
B : Diborates
B : Neso-diborates with double tetrahedra B2O(OH)6; 2(2T)
26.2.1.1
26 : HYDRATED BORATES CONTAINING HYDROXYL OR HALOGEN
2 : Diborates
26 : HYDRATED BORATES CONTAINING HYDROXYL OR HALOGEN
2 : Diborates
9.3.15
9 : Borates
3 : Borates of Ca and Sr
9 : Borates
3 : Borates of Ca and Sr
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 |
|---|---|---|
| Phb | 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 Pentahydroborite
Vitreous
Transparency:
Transparent
Colour:
Colourless
Streak:
White
Hardness:
2½ on Mohs scale
Cleavage:
None Observed
Density:
2.00 - 2.03 g/cm3 (Measured) 2.02 g/cm3 (Calculated)
Optical Data of Pentahydroborite
Type:
Biaxial (+)
RI values:
nα = 1.531\0 - 1.532 nβ = 1.536 - 1.539 nγ = 1.542 - 1.546
2V:
Measured: 73° to 79°
Max. Birefringence:
δ = 0.010 - 0.014
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:
None to Very Low
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 biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Dispersion:
r < v moderate
Chemistry of Pentahydroborite
Mindat Formula:
CaB2O(OH)6 · 2H2O
Element Weights:
Elements listed:
Crystallography of Pentahydroborite
Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 7.845(4) Å, b = 6.525(5) Å, c = 8.124(5) Å
α = 111.62(5)°, β = 111.19(4)°, γ = 73.44(6)°
α = 111.62(5)°, β = 111.19(4)°, γ = 73.44(6)°
Ratio:
a:b:c = 1.202 : 1 : 1.245
Unit Cell V:
354.89 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Anhedral granular.
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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CIF File Best | x | y | z | a | b | c
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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) |
|---|---|---|---|---|---|---|---|
| 0015573 | Pentahydroborite | Kazanskaya E V, Chemodina T N, Egorov-Tismenko Y K, Simonov M A, Belov N V (1977) Refined crystal structure of pentahydroborite Ca(B2O(OH)6)*(H2O)2 Soviet Physics Crystallography 22 35-36 | 1977 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 7.04 Å | (10) |
| 2.99 Å | (9) |
| 3.54 Å | (8) |
| 1.937 Å | (8) |
| 2.88 Å | (6) |
| 3.20 Å | (5) |
| 2.49 Å | (5) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47c : [Carbonates, phosphates, borates, nitrates] | |
| Stage 10a: Neoproterozoic oxygenation/terrestrial biosphere | <0.6 |
| 48 : Soil leaching zone minerals | <0.6 |
| Stage 10b: Anthropogenic minerals | <10 Ka |
| 55 : Anthropogenic mine minerals |
Type Occurrence of Pentahydroborite
General Appearance of Type Material:
Small grains showing no crystal form
Place of Conservation of Type Material:
All-Union Research Institute of Mineral Resources, Moscow, Russia.
Associated Minerals at Type Locality:
Other Language Names for Pentahydroborite
Dutch:Pentahydroboriet
German:Pentahydroborit
Japanese:五水灰硼石
Russian:Пентагидроборит
Spanish:Pentahydroborita
Common Associates
Associations Based on Photo Data:
| 13 photos of Pentahydroborite associated with Andradite | Ca3Fe3+2(SiO4)3 |
| 13 photos of Pentahydroborite associated with Galena | PbS |
| 13 photos of Pentahydroborite associated with Wurtzite | (Zn,Fe)S |
| 4 photos of Pentahydroborite associated with Henmilite | Ca2Cu[B(OH)4]2(OH)4 |
| 2 photos of Pentahydroborite associated with Calcite | CaCO3 |
| 1 photo of Pentahydroborite associated with Frolovite | Ca[B(OH)4]2 |
| 1 photo of Pentahydroborite associated with Charlesite | Ca6(Al,Si)2(SO4)2[B(OH)4](OH,O)12 · 26H2O |
Related Minerals - Strunz-mindat Grouping
| 6.BB.05 | Pinnoite | Mg[B2O(OH)6] |
Fluorescence of Pentahydroborite
Violet in long wave UV
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 Pentahydroborite
mindat.org URL:
https://www.mindat.org/min-3154.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Pentahydroborite
Reference List:
Fleischer, Michael; František, Čech (1962) New mineral names. American Mineralogist, 47 (11-12). 1482-1485
IMA (1967) International Mineralogical Association: Commission on New Minerals and Mineral Names. Mineralogical Magazine and Journal of the Mineralogical Society, 36 (277) 131-136 doi:10.1180/minmag.1967.036.277.20
Localities for Pentahydroborite
Showing 6 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.
China | |
| Fabre (n.d.) +1 other reference |
Japan | |
| Fujiwara et al. (1982) +3 other references |
Kazakhstan | |
| Handbook of Mineralogy - ... |
Russia | |
| [AmMin 85:1322] +2 other references |
| American Mineralogist: 85: 1322. +3 other references |
Serbia | |
| Malinko et al. (2004) |
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Fuka mine, Fuka, Bitchū, Takahashi City, Okayama Prefecture, Japan