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Isoclasite
A valid IMA mineral species - grandfathered - questionable
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Formula:
Ca2(PO4)(OH) · 2H2O
Colour:
colourless, snow-white; colourless in transmitted light.
Lustre:
Vitreous, Pearly
Hardness:
1 - 1½
Specific Gravity:
2.92
Crystal System:
Monoclinic
Name:
From the Greek for "equal fracture," in allusion to the cleavage.
This page provides mineralogical data about Isoclasite.
Unique Identifiers
Mindat ID:
2051
Long-form identifier:
mindat:1:1:2051:6
IMA Classification of Isoclasite
Approved, 'Grandfathered' (first described prior to 1959), Questionable
IMA Formula:
Ca2PO4(OH)·2H2O
Classification of Isoclasite
8.DN.10
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
N : With only large cations
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
N : With only large cations
42.6.2.1
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
6 : A2(XO4)Zq·xH2O
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
6 : A2(XO4)Zq·xH2O
19.4.4
19 : Phosphates
4 : Phosphates of Ca
19 : Phosphates
4 : Phosphates of Ca
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 |
|---|---|---|
| Icl | 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 Isoclasite
Vitreous, Pearly
Transparency:
Transparent
Comment:
Lustre pearly on cleavages.
Colour:
Colourless, snow-white; colourless in transmitted light.
Hardness:
1 - 1½ on Mohs scale
Cleavage:
Distinct/Good
On {010}, distinct.
On {010}, distinct.
Density:
2.92 g/cm3 (Measured)
Optical Data of Isoclasite
Type:
Biaxial (+)
RI values:
nα = 1.565 nβ = 1.568 nγ = 1.580
2V:
Calculated: 54°
Max. Birefringence:
δ = 0.015
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:
Moderate (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 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 strong
Chemistry of Isoclasite
Mindat Formula:
Ca2(PO4)(OH) · 2H2O
Element Weights:
Elements listed:
Crystallography of Isoclasite
Crystal System:
Monoclinic
Morphology:
Crystals minute, dull, prismatic [001]; also occurs as cotton-like fibers.
Comment:
inferred from optical data
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] |
Type Occurrence of Isoclasite
General Appearance of Type Material:
Transparent crystals, to 4 cm in length, partly altered to a milky colored material.
Geological Setting of Type Material:
Reddish dolomite vein in hornfels.
Associated Minerals at Type Locality:
Other Language Names for Isoclasite
Common Associates
Associations Based on Photo Data:
| 1 photo of Isoclasite associated with Fluorapatite | Ca5(PO4)3F |
Related Minerals - Strunz-mindat Grouping
| 8.DN. | Loomisite | Ba[Be2P2O8] · H2O |
| 8.DN.05 | Natrophosphate | Na6+xHxF(PO4)2 · (19+x)H2O |
| 8.DN.15 | 'Urphoite' | U4+6(PO4)7(OH)3 · 4H2O |
| 8.DN.15 | Lermontovite | U(PO4)(OH) · H2O |
| 8.DN.20 | Vyacheslavite | U(PO4)(OH) |
Other Information
Notes:
Readily soluble in acids.
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 Isoclasite
mindat.org URL:
https://www.mindat.org/min-2051.html
Please feel free to link to this page.
Please feel free to link to this page.