Mindat Logo

Acuminite

This page is currently not sponsored. Click here to sponsor this page.



Formula:
Sr[AlF
 
4
(OH)(H
 
2
O)]
System:MonoclinicColour:Colourless, white, ...
Hardness:
Name:From Latin "acumen", "spearhead", in allusion to the shape of its crystals.


An aluminium complex salt. Only found in two cavities in a single specimen 10,5 cm across.

Classification of Acuminite

IMA status:Approved 1986
Strunz 8th edition ID:3/C.01-20
Strunz 9th edition ID:3.CC.10
Nickel-Strunz 10th (pending) edition ID:3.CC.10

3 : HALIDES
C : Complex halides
C : Soro-aluminofluorides
Dana 8th edition ID:11.6.17.1

11 : HALIDE COMPLEXES
6 : Aluminofluorides - Isolated Octahedra
Hey's CIM Ref.:8.4.15

8 : Halides - Fluorides, Chlorides, Bromides and Iodides; also Fluoborates and Fluosilicates
4 : Halides of the alkaline earths and Mg
mindat.org URL:http://www.mindat.org/min-19.html
Please feel free to link to this page.

Type Occurrence of Acuminite

Type Locality:Ivigtut Cryolite deposit, Ivittuut (Ivigtut), Arsuk Fjord, Sermersooq, Greenland
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:
ThomsenoliteRalstonitePachnoliteJarliteGearksutite
FluoriteCelestine

Physical Properties of Acuminite

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

Crystallography of Acuminite

Crystal System:Monoclinic
Cell Parameters:a = 13.223Å, b = 5.175Å, c = 14.251Å
β = 11.61°
Ratio:a:b:c = 2.555 : 1 : 2.754
Unit Cell Volume:V 196.25 ų (Calculated from Unit Cell)
Z:8
Morphology:{110}, {_111}, rarely {_112}
Twinning:on {100}, as contact twins
X-Ray Powder Diffraction:
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

Optical Data of Acuminite

Type:Biaxial (+)
RI values: nα = 1.451 nβ = 1.453 nγ = 1.462 - 1.463
2V:Measured: 46° to 57°, Calculated: 50° to 52°
Maximum Birefringence:δ = 0.012

Chart 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 Acuminite

Formula:
Sr[AlF
 
4
(OH)(H
 
2
O)]
Simplified for copy/paste:Sr[AlF4(OH)(H2O)]
Essential elements:Al, F, H, O, Sr
All elements listed in formula:Al, F, H, O, Sr
Analytical Data:Ca and Sr determined by atomic absorption spectroscopy (AA), Al by CDTA, F electrochemically; OH calculated from the charge balance, H2O from theory
Ca (0.02)
Sr (37.04)
Al (11.86)
F (33.52)
OH (6.82)
H2O (7.80)

sum 97.06 wt.-%
Empirical Formula:
Sr
 
0.98
Al
 
1.02
F
 
4.07
(OH)
 
0.93
· 1.00H
 
2
O
Common Impurities:Ca

Relationship of Acuminite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
3.CC.05Gearksutite
Ca[Al(F,OH)
 
5
(H
 
2
O)]
3.CC.10Tikhonenkovite
Sr[AlF
 
4
(OH)(H
 
2
O)]
3.CC.15Artroeite
Pb[AlF
 
3
(OH)
 
2
]
3.CC.20Calcjarlite
Na(Ca,Sr)
 
3
Al
 
3
(OH)
 
2
F
 
14
3.CC.20Jarlite
Na(Sr,Na)
 
7
MgAl
 
6
F
 
32
(OH,H
 
2
O)
 
2
3.CC.20Jørgensenite
Na
 
2
(Sr,Ba)
 
14
Na
 
2
Al
 
12
F
 
64
(OH,F)
 
4
Related Minerals - Hey's Index Grouping:

- +
8.4.1Sellaite
MgF
 
2
8.4.2Neighborite
NaMgF
 
3
8.4.3Bischofite
MgCl
 
2
· 6H
 
2
O
8.4.4Korshunovskite
Mg
 
2
Cl(OH)
 
3
· 4H
 
2
O
8.4.5Carnallite
KMgCl
 
3
· 6H
 
2
O
8.4.6Tachyhydrite
CaMg
 
2
Cl
 
6
· 12H
 
2
O
8.4.7Fluorite
CaF
 
2
8.4.8Sinjarite
CaCl
 
2
· 2H
 
2
O
8.4.9Antarcticite
CaCl
 
2
· 6H
 
2
O
8.4.10Chlorocalcite
KCaCl
 
3
8.4.11Rorisite
CaFCl
8.4.12Jarlite
Na(Sr,Na)
 
7
MgAl
 
6
F
 
32
(OH,H
 
2
O)
 
2
8.4.13Calcjarlite
Na(Ca,Sr)
 
3
Al
 
3
(OH)
 
2
F
 
14
8.4.14Tikhonenkovite
Sr[AlF
 
4
(OH)(H
 
2
O)]
8.4.16Frankdicksonite
BaF
 
2
8.4.17Usovite
Ba
 
2
CaMgAl
 
2
F
 
14
8.4.18Bøgvadite
Na
 
2
SrBa
 
2
Al
 
4
F
 
20

Other Names for Acuminite

Synonyms:
IMA1986-038
Other Languages:
Dutch:Acuminiet
German:Acuminit
Italian:Acuminite
Latvian:Akuminīts
Portuguese:Acuminite
Russian:Акуминит
Spanish:Acuminita

Other Information

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

References for Acuminite

Reference List:

- +
Pauly, H. and Petersen, O. V. (1987) Acuminite, a new Sr fluoride from Ivigtut, South Greenland. Neues Jahrbuch für Mineralogie, Monatshefte, 502-514. - American Mineralogist (1988), 73, 1492 (abstract).

Krogh Andersen, E., Ploug-Sorensen, G. and Leonardsen, E. (1991) The structure of acuminite, a strontium aluminium fluoride mineral. Zeitschrift für Kristallographie 194, 221-227.

Anthony, J. W. et al. (1997) Handbook of Mineralogy, Vol. 3, 2.

Internet Links for Acuminite

Search Engines:
  • Look for Acuminite on Google
  • Look for Acuminite images on Google
  • External Links:
  • Look for Acuminite on Webmineral
  • Look for Acuminite on Athena Mineralogy
  • Look for Acuminite on Wikipedia
  • Look for Acuminite on Mineralien Atlas
  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Acuminite details from Handbook of Mineralogy (PDF)
  • Mineral Dealers:
  • Buy rare minerals from Excalibur Minerals
  • Buy RARE Minerals from Rocks of Africa
  • Buy from Dave Bunk Minerals
  • Lapis Mineral Magazin
  • Fine minerals from bisbeeborn.com
  • The Arkenstone - Fine Minerals
  • rare and unusual minerals mainly crystallized
  • Acuminite specimens for sale - minfind.com
  • Fine and rare minerals from mintreasure.com
  • Fine Minerals from Weinrich Minerals, Inc.
  • Buy from McDougall Minerals
  • DAKOTA MATRIX offers Cabinet and Rare Species from Worldwide Localities.
  • Localities for Acuminite

    The 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.
    (TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
    Greenland
     
    • Sermersooq
      • Arsuk Fjord
        • Ivittuut (Ivigtut)
    [Neues Jahrb.Min.,Mh.(1987) 502-514; Nickel & Nichols, 1991]; Petersen, O. V and K Secher (1993) The Minerals of Greenland. Mineralogical Record 24:36
    Mineral and/or Locality  
    Search Google  
    Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
    Current server date and time: August 6, 2014 21:33:39
    Mineral and Locality Search
    Mineral:
    and/or Locality:
    Options
    Fade toolbar when not in focusFix toolbar to bottom of page
    Hide Social Media Links
    Slideshow frame delay seconds