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Acuminite

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Formula:
Sr[AlF4(OH)(H2O)]
Colour:
Colourless, white, becomes yellow on exposure to x-rays
Lustre:
Vitreous
Hardness:
Specific Gravity:
3.295
Crystal System:
Monoclinic
Name:
From Latin "acumen", "spearhead", in allusion to the shape of its crystals.
Dimorph of:
An aluminium 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.


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Classification of AcuminiteHide

Approved
Approval Year:
1986
3.CC.10

3 : HALIDES
C : Complex halides
C : Soro-aluminofluorides
11.6.17.1

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

Physical Properties of AcuminiteHide

Vitreous
Transparency:
Transparent
Colour:
Colourless, white, becomes yellow on exposure to x-rays
Streak:
white
Hardness:
3½ on Mohs scale
Cleavage:
Perfect
on {001}
Density:
3.295 g/cm3 (Measured)    3.305 g/cm3 (Calculated)

Optical Data of AcuminiteHide

Type:
Biaxial (+)
RI values:
nα = 1.451 nβ = 1.453 nγ = 1.462 - 1.463
2V:
Measured: 46° to 57°, Calculated: 50° to 52°
Max Birefringence:
δ = 0.012
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
Moderate
Dispersion:
r > v, strong

Chemical Properties of AcuminiteHide

Formula:
Sr[AlF4(OH)(H2O)]
IMA Formula:
SrAlF4(OH) · H2O
Common Impurities:
Ca

Crystallography of AcuminiteHide

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/b
Setting:
C2/c
Cell Parameters:
a = 13.223 Å, b = 5.175 Å, c = 14.251 Å
β = 11.61°
Ratio:
a:b:c = 2.555 : 1 : 2.754
Unit Cell V:
196.25 ų (Calculated from Unit Cell)
Z:
8
Morphology:
{110}, {_111}, rarely {_112}
Twinning:
on {100}, as contact twins

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
2.075 (9)
3.286 (8)
3.310 (8)
3.353 (10)
3.505 (10)
4.706 (10)
4.767 (10)
Comments:
Recorded on type material

Type Occurrence of AcuminiteHide

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 AcuminiteHide

Other Language Names for AcuminiteHide

Dutch:Acuminiet
German:Acuminit
Italian:Acuminite
Latvian:Akuminīts
Portuguese:Acuminite
Spanish:Acuminita

Related Minerals - Nickel-Strunz GroupingHide

3.CC.05GearksutiteCa[Al(F,OH)5(H2O)]Tric. 1 : P1
3.CC.10TikhonenkoviteSr[AlF4(OH)(H2O)]Mon. 2/m : P21/b
3.CC.15ArtroeitePb[AlF3(OH)2]Tric. 1 : P1
3.CC.20CalcjarliteNa(Ca,Sr)3Al3(OH)2F14Mon.
3.CC.20JarliteNa(Sr,Na)7MgAl6F32(OH,H2O)2Mon. 2/m
3.CC.20JørgenseniteNa2(Sr,Ba)14Na2Al12F64(OH,F)4Mon. 2/m

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

8.4.1SellaiteMgF2Tet. 4/mmm (4/m 2/m 2/m) : P42/mnm
8.4.2NeighboriteNaMgF3Orth. mmm (2/m 2/m 2/m)
8.4.3BischofiteMgCl2 · 6H2OMon. 2/m : B2/m
8.4.4KorshunovskiteMg2Cl(OH)3 · 4H2OTric.
8.4.5CarnalliteKMgCl3 · 6H2OOrth. mmm (2/m 2/m 2/m) : Pnna
8.4.6TachyhydriteCaMg2Cl6 · 12H2OTrig.
8.4.7FluoriteCaF2Iso. m3m (4/m 3 2/m) : Fm3m
8.4.8SinjariteCaCl2 · 2H2OTet.
8.4.9AntarcticiteCaCl2 · 6H2OTrig. 3 2 : P3 2 1
8.4.10ChlorocalciteKCaCl3Orth. mmm (2/m 2/m 2/m) : Pnma
8.4.11RorisiteCaFClTet.
8.4.12JarliteNa(Sr,Na)7MgAl6F32(OH,H2O)2Mon. 2/m
8.4.13CalcjarliteNa(Ca,Sr)3Al3(OH)2F14Mon.
8.4.14TikhonenkoviteSr[AlF4(OH)(H2O)]Mon. 2/m : P21/b
8.4.16FrankdicksoniteBaF2Iso. m3m (4/m 3 2/m) : Fm3m
8.4.17UsoviteBa2CaMgAl2F14Mon.
8.4.18BøgvaditeNa2SrBa2Al4F20Mon. 2/m

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for AcuminiteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Pauly, H., Petersen, O.V. (1987) Acuminite, a new Sr fluoride from Ivigtut, South Greenland. Neues Jahrbuch für Mineralogie, Monatshefte: 1987: 502-514.
Jambor, J.L., Burke, E.A.J., Ercrit, S., Grice, J.D. (1988) New mineral names. American Mineralogist: 73: 1492-1499.
Krogh Andersen, E., Ploug-Sorensen, G., Leonardsen, E. (1991) The structure of acuminite, a strontium aluminium fluoride mineral. Zeitschrift für Kristallographie: 194: 221-227.
Jambor, J.L., Vanko, D.A. (1992) New mineral names. American Mineralogist: 77: 446-452.
Anthony, J.W. et al. (1997) Handbook of Mineralogy, Vol. 3, 2.

Internet Links for AcuminiteHide

Localities for AcuminiteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for 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). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
Greenland (TL)
 
  • Sermersooq
    • Arsuk Fjord
      • Ivittuut (Ivigtut)
[Neues Jahrb.Min.,Mh.(1987) 502-514; Nickel & Nichols, 1991]; Petersen, O.V. and Secher, K. (1993): The minerals of Greenland. Mineralogical Record 24 (2): 1-65 (p.36)
Mineral and/or Locality  
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