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Ernstite
A valid IMA mineral species
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About Ernstite
Formula:
(Mn2+,Fe3+)Al(PO4)(OH,O)2 · H2O
Colour:
Yellow-brown
Hardness:
3 - 3½
Specific Gravity:
3.07
Crystal System:
Monoclinic
Name:
Named for Dr. Karl Theodor Heinrich Ernst ((3 January 1904, Uelzen, Germany - 26 February 1983, Erlangen, Germany), professor of mineralogy, Erlangen University, Erlangen, Germany.
Ernstite was named on oxidized eosphorite. As eosphorite has by definition Mn2+ > Fe2+, then the ferric component could never be greater than 50 mole percent and is therefore only a named variety. Some of the water molecule occupancy in the empirical eosphorite formula may be converted to hydroxyl in the same ratio as the oxidized Fe. The above formula shows only hydroxyl plus oxygen in the formula instead of (OH, O, H20) as though oxygen and hydroxyl were in equivalent sites without any residual water in the structure. If the actual original material were a childrenite, it would be possible to have a ferric-dominant oxidized member of the series. No name has been proposed for oxidized childrenite, but any such new name would have to have ferric iron > 50 mole percent of the M site. Ernstite should be re-investigated.
Unique Identifiers
Mindat ID:
1404
Long-form identifier:
mindat:1:1:1404:1
IMA Classification of Ernstite
Approved
IMA Formula:
(Mn2+,Fe3+)AlPO4(OH,O)2
Approval year:
1970
First published:
1970
Approval history:
IMA1970-012
Classification of Ernstite
8.DD.20
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
42.7.1.3
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
7 : (AB)2(XO4)Zq·xH2O
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
7 : (AB)2(XO4)Zq·xH2O
19.12.56
19 : Phosphates
12 : Phosphates of Mn
19 : Phosphates
12 : Phosphates of Mn
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 |
|---|---|---|
| Ens | 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 Ernstite
Transparency:
Translucent
Colour:
Yellow-brown
Hardness:
3 - 3½ on Mohs scale
Cleavage:
Distinct/Good
Very Good on {100}
Good on {010}
Very Good on {100}
Good on {010}
Density:
3.07 g/cm3 (Measured) 3.086 g/cm3 (Calculated)
Optical Data of Ernstite
Type:
Biaxial (-)
RI values:
nα = 1.678 nβ = 1.706 nγ = 1.721
2V:
Measured: 74° , Calculated: 70°
Max. Birefringence:
δ = 0.043
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 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
Pleochroism:
Visible
Comments:
X= yellowish-brown
Y= red-brown
Z= pale yellow
Y= red-brown
Z= pale yellow
Chemistry of Ernstite
Mindat Formula:
(Mn2+,Fe3+)Al(PO4)(OH,O)2 · H2O
Element Weights:
Crystallography of Ernstite
Crystal System:
Monoclinic
Cell Parameters:
a = 13.32(1) Å, b = 10.497(5) Å, c = 6.969(4) Å
β = 90.37°
β = 90.37°
Ratio:
a:b:c = 1.269 : 1 : 0.664
Unit Cell V:
974.39 ų (Calculated from Unit Cell)
Z:
8
Morphology:
Radial aggregates
Comment:
Point group: 2/m or m; space group: A2/a or Aa.
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 4.364 Å | (40) |
| 3.516 Å | (40) |
| 2.836 Å | (80) |
| 2.829 Å | (100) |
| 2.438 Å | (50) |
| 2.424 Å | (40) |
| 2.001 Å | (40) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 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] |
Type Occurrence of Ernstite
Place of Conservation of Type Material:
National Museum of Natural History, Washington, D.C., USA, 145620.
Geological Setting of Type Material:
Oxidized granitic pegmatite
Associated Minerals at Type Locality:
Synonyms of Ernstite
Other Language Names for Ernstite
Common Associates
Associations Based on Photo Data:
| 10 photos of Ernstite associated with Eosphorite | Mn2+Al(PO4)(OH)2 · H2O |
| 2 photos of Ernstite associated with Kosnarite | KZr2(PO4)3 |
| 1 photo of Ernstite associated with Chlorapatite | Ca5(PO4)3Cl |
| 1 photo of Ernstite associated with Siderite | FeCO3 |
Related Minerals - Strunz-mindat Grouping
| 8.DD. | Penberthycroftite | [Al6(AsO4)3(OH)9(H2O)5] · 8H2O |
| 8.DD. | Bettertonite | [Al6(AsO4)3(OH)9(H2O)5] · 11H2O |
| 8.DD. | Vargite | MnCu2Mn2(AsO4)2(OH)4(H2O)4 |
| 8.DD. | Galeaclolusite | Al6(AsO4)3(OH)9(H2O)4 · 8H2O |
| 8.DD.05 | Luetheite | Cu2Al2(AsO4)2(OH)4 |
| 8.DD.05 | Chenevixite | Cu2Fe3+2(AsO4)2(OH)4 |
| 8.DD.10 | Akrochordite | MnMn2Mn2(AsO4)2(OH)4(H2O)4 |
| 8.DD.10 | Guanacoite | MgCu2Mg2(AsO4)2(OH)4(H2O)4 |
| 8.DD.15 | 'UM1981-32-PO:FeH' | Fe2+Fe3+6(PO4)4-x[PO3(OH)]x(OH)8 · 4H2O |
| 8.DD.15 | Afmite | Al3(OH)4(H2O)3(PO4)(PO3OH) · H2O |
| 8.DD.15 | Aheylite | (Fe2+,Zn)Al6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | 'Coeruleolactite' | |
| 8.DD.15 | Faustite | ZnAl6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | Planerite | Al6(PO4)2(PO3OH)2(OH)8 · 4H2O |
| 8.DD.15 | Chalcosiderite | CuFe3+6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | Turquoise | CuAl6(PO4)4(OH)8 · 4H2O |
| 8.DD.20 | Eosphorite | Mn2+Al(PO4)(OH)2 · H2O |
| 8.DD.20 | Lefontite | Fe2Al2Be(PO4)2(OH)6 |
| 8.DD.20 | Childrenite | Fe2+Al(PO4)(OH)2 · H2O |
| 8.DD.25 | Kobokoboite | Al6(PO4)4(OH)6 · 11H2O |
| 8.DD.30 | Smamite | Ca2Sb(OH)4[H(AsO4)2] · 6H2O |
| 8.DD.35 | 'Gutsevichite' | Al3(PO4)2(OH)3 · 8H2O |
| 8.DD.40 | 'Laubmannite (of Moore)' | (Fe3+,Fe2+,M)8+x(OH,H2O)9(H2O)2(PO4)5, M = Fe3+, Cu2+ or other metal cation, x ~ 0.1. |
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 Ernstite
mindat.org URL:
https://www.mindat.org/min-1404.html
Please feel free to link to this page.
Please feel free to link to this page.
Search Engines:
External Links:
Mineral Dealers:
St Johns Quarry, St Johns, Light Regional Council, South Australia, Australia