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Jahnsite-(CaFeMg)
A valid IMA mineral species
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About Jahnsite-(CaFeMg)
Richard H. Jahns
Formula:
{Ca}{Fe2+}{Mg2}{Fe3+2}(PO4)4(OH)2 · 8H2O
Colour:
Brownish orange
Lustre:
Vitreous
Hardness:
4
Specific Gravity:
2.76
Crystal System:
Monoclinic
Member of:
Name:
The root name is in honor of Richard Henry Jahns (March 10, 1915 Los Angeles, California, USA - December 31, 1983 Palo Alto, California, USA), mineralogist and pegmatite expert, Stanford University, Palo Alto, California, USA. The suffix indicates metal site occupancies.
Unique Identifiers
Mindat ID:
46052
Long-form identifier:
mindat:1:1:46052:7
Similar Names
| Jahnsite | A synonym of Jahnsite Subgroup | |
| Jahnsite-(CaFeFe) | Valid as an unnamed mineral | {Ca}{Fe2+}{Fe22+}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(CaMgMg) | Valid as an unnamed mineral | {Ca}{Mg}{Mg2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(CaMnFe) | A valid IMA mineral species | {Ca}{Mn2+}{Fe22+}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(CaMnMg) | A valid IMA mineral species | {Ca}{Mn2+}{(Mg,Fe2+)2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(CaMnMn) | A valid IMA mineral species | {Ca}{Mn2+}{Mn22+}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(CaMnZn) | A valid IMA mineral species | {Ca}{Mn2+}{Zn2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(MnMnFe) | A valid IMA mineral species | {Mn2+}{Mn2+}{Fe22+}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(MnMnMg) | A valid IMA mineral species | {Mn2+}{Mn2+}{Mg2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(MnMnMn) | A valid IMA mineral species | {Mn2+}{Mn2+}{Mn22+}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(MnMnZn) | A valid IMA mineral species | {Mn2+}{Mn2+}{Zn2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(NaFeMg) | A valid IMA mineral species | {Na}{Fe3+}{Mg2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(NaMnMg) | A valid IMA mineral species | {(Na,Ca)}{(Mn2+,Fe3+)}{(Mg,Fe3+)2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Jahnsite-(NaMnMn) | A valid IMA mineral species | {Na}{Mn2+}{(Mn2+,Fe3+)2}{Fe23+}(PO4)4(OH)2 · 8H2O |
| Janosite | A synonym of Copiapite | |
| Jonesite | A valid IMA mineral species | Ba4(K,Na)2Ti4Al2(Si3O9)2(SiO4)4O2 · 6H2O |
Classification of Jahnsite-(CaFeMg)
The jahnsite structure archetype
The structure archetype of jahnsite group minerals, which includes the jahnsite and whiteite subgroups.
IMA Classification of Jahnsite-(CaFeMg)
Approved
IMA Formula:
CaFe2+Mg2Fe3+2(PO4)4(OH)2·8H2O
Approval year:
2013
First published:
2016
Type description reference:
8.DH.15
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
H : With large and medium-sized cations, (OH, etc.):RO4 < 1:1
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
H : With large and medium-sized cations, (OH, etc.):RO4 < 1:1
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Jah-CaFeMg | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
| Jhn | The Canadian Mineralogist (2019) | The Canadian Mineralogist (2019) The Canadian Mineralogist list of symbols for rock- and ore-forming minerals (December 30, 2019). download |
Physical Properties of Jahnsite-(CaFeMg)
Vitreous
Transparency:
Transparent
Colour:
Brownish orange
Streak:
White
Hardness:
4 on Mohs scale
Comment:
ca. 4
Tenacity:
Brittle
Cleavage:
Distinct/Good
{001}
{001}
Fracture:
Splintery
Density:
2.76(4) g/cm3 (Measured) 2.772 g/cm3 (Calculated)
Optical Data of Jahnsite-(CaFeMg)
Type:
Biaxial (-)
RI values:
nα = 1.629(4) nβ = 1.658(4) nγ = 1.677(4)
2V:
Calculated: 76.8°
Max. Birefringence:
δ = 0.048
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:
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 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.
Chemistry of Jahnsite-(CaFeMg)
Mindat Formula:
{Ca}{Fe2+}{Mg2}{Fe3+2}(PO4)4(OH)2 · 8H2O
Element Weights:
Crystallography of Jahnsite-(CaFeMg)
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P2/b
Setting:
P2/a
Cell Parameters:
a = 14.975(5) Å, b = 7.1645(14) Å, c = 9.928(2) Å
β = 110.65(3)°
β = 110.65(3)°
Ratio:
a:b:c = 2.09 : 1 : 1.386
Unit Cell V:
996.72 ų (Calculated from Unit Cell)
Z:
2
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 9.339 Å | (100) |
| 4.923 Å | (20) |
| 3.562 Å | (20) |
| 3.518 Å | (20) |
| 3.453 Å | (20) |
| 2.965 Å | (20) |
| 2.839 Å | (35) |
| 2.592 Å | (20) |
Reference:
Comments:
From Type Description.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 21 : Chemically precipitated carbonate, phosphate, iron formations | |
| 22 : Hydration and low-? subsurface aqueous alteration (see also #23) | |
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 34 : Complex granite pegmatites | |
| 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 |
| 50 : Coal and/or oil shale minerals | <0.36 |
Type Occurrence of Jahnsite-(CaFeMg)
General Appearance of Type Material:
Prisms, up to 0.2 mm
Place of Conservation of Type Material:
Type material is deposited in the collections of the S
Tom's Quarry, Koonunga, Light Regional Council, South Australia, Australia