Acuminite
A valid IMA mineral species
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Formula:
Sr[AlF4(OH)(H2O)]
Colour:
Colourless, white, becomes yellow on exposure to x-rays
Lustre:
Vitreous
Hardness:
3½
Specific Gravity:
3.295
Crystal System:
Monoclinic
Name:
From Latin "acumen", "spearhead", in allusion to the shape of its crystals.
Dimorph of:
An aluminum complex salt. Only found in two cavities in a single specimen 10.5 cm across.
Chemically identical and structurally similar to tikhonenkovite.
Structure details (Krogh Andersen et al., 1991): SrF7(H2O)2 and AlF4(OH)2 polyhedra link to form puckered layers || (010). One Sr polyhedron links to three other polyhedrons. Structure differs from that of tikhonenkovite in type of this connection, which is two edge connections and one apex sharing against one edge and two apex connections in tikhonenkovite.
Chemically identical and structurally similar to tikhonenkovite.
Structure details (Krogh Andersen et al., 1991): SrF7(H2O)2 and AlF4(OH)2 polyhedra link to form puckered layers || (010). One Sr polyhedron links to three other polyhedrons. Structure differs from that of tikhonenkovite in type of this connection, which is two edge connections and one apex sharing against one edge and two apex connections in tikhonenkovite.
Unique Identifiers
Mindat ID:
19
Long-form identifier:
mindat:1:1:19:8
Similar Names
| Aluminite | A valid IMA mineral species - grandfathered | Al2(SO4)(OH)4 · 7H2O |
IMA Classification of Acuminite
Approved
IMA Formula:
SrAlF4(OH)·H2O
Approval year:
1986
First published:
1987
Classification of Acuminite
3.CC.10
3 : HALIDES
C : Complex halides
C : Soro-aluminofluorides
3 : HALIDES
C : Complex halides
C : Soro-aluminofluorides
11.6.17.1
11 : HALIDE COMPLEXES
6 : Aluminofluorides - Isolated Octahedra
11 : HALIDE COMPLEXES
6 : Aluminofluorides - Isolated Octahedra
8.4.15
8 : Halides - Fluorides, Chlorides, Bromides and Iodides; also Fluoborates and Fluosilicates
4 : Halides of the alkaline earths and Mg
8 : Halides - Fluorides, Chlorides, Bromides and Iodides; also Fluoborates and Fluosilicates
4 : Halides of the alkaline earths and Mg
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 |
|---|---|---|
| Acu | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
| Ac | 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 Acuminite
Vitreous
Transparency:
Transparent
Colour:
Colourless, white, becomes yellow on exposure to x-rays
Streak:
White
Hardness:
3½ on Mohs scale
Cleavage:
Perfect
on {001}
on {001}
Density:
3.295 g/cm3 (Measured) 3.305 g/cm3 (Calculated)
Optical Data of Acuminite
Type:
Biaxial (+)
RI values:
nα = 1.4507 nβ = 1.4528 nγ = 1.4624 - 1.4627
2V:
Measured: 46° to 57°, Calculated: 50° to 52°
Max. Birefringence:
δ = 0.012
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.
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.
Surface Relief:
Moderate
Dispersion:
r > v, strong
Chemistry of Acuminite
Mindat Formula:
Sr[AlF4(OH)(H2O)]
Element Weights:
Common Impurities:
Ca
Crystallography of Acuminite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/b
Setting:
C2/c
Cell Parameters:
a = 13.223(1) Å, b = 5.175(1) Å, c = 14.251(1) Å
β = 111.61(2)°
β = 111.61(2)°
Ratio:
a:b:c = 2.555 : 1 : 2.754
Unit Cell V:
906.64 ų (Calculated from Unit Cell)
Z:
8
Morphology:
{110}, {111}, rarely {112}
Twinning:
on {100}, as contact twins
Crystal Structure
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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) |
|---|---|---|---|---|---|---|---|
| 0010999 | Acuminite | Krogh Andersen E, Ploug-Sorensen G, Leonardsen E (1991) The structure of acuminite, a strontium aluminium fluoride mineral Zeitschrift fur Kristallographie 194 221-227 |  | 1991 | Ivigtut, Greenland | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 2.075 Å | (9) |
| 3.286 Å | (8) |
| 3.310 Å | (8) |
| 3.353 Å | (10) |
| 3.505 Å | (10) |
| 4.706 Å | (10) |
| 4.767 Å | (10) |
Comments:
Recorded on type material
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 25 : Evaporites (prebiotic) |
Type Occurrence of Acuminite
General Appearance of Type Material:
Acute dipyramidal crystals, resembling spear points, to 1 mm.
Place of Conservation of Type Material:
University of Copenhagen, Copenhagen, Denmark.
Geological Setting of Type Material:
Strontium-rich portion of a cryolite deposit.
Associated Minerals at Type Locality:
Synonyms of Acuminite
Other Language Names for Acuminite
Related Minerals - Strunz-mindat Grouping
| 3.CC.05 | Gearksutite | Ca[Al(F,OH)5(H2O)] |
| 3.CC.10 | Tikhonenkovite | Sr[AlF4(OH)(H2O)] |
| 3.CC.15 | Artroeite | Pb[AlF3(OH)2] |
| 3.CC.20 | Jarlite | Na(Sr,Na)7MgAl6F32(OH,H2O)2 |
| 3.CC.20 | Calcjarlite | Na(Ca,Sr)3Al3(OH)2F14 |
| 3.CC.20 | Jørgensenite | Na2(Sr,Ba)14Na2Al12F64(OH,F)4 |
Other Information
Notes:
Becomes yellow on exposure to X-rays.
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 Acuminite
mindat.org URL:
https://www.mindat.org/min-19.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Acuminite
Reference List:
Jambor, John L., Ercit, Ernst A. J. Burke T. Scott, Grice, Joel D. (1988) New Mineral Names. American Mineralogist, 73 (11-12) 1492-1499
Localities for Acuminite
Showing 1 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.
Greenland (TL) | |
| Pauly et al. (1987) +2 other references |
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