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Oligoclase

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Formula:
(Na,Ca)[Al(Si,Al)Si2O8]
Colour:
Colourless, white, very ...
Hardness:
6 - 6½
Member of:
Name:
Named in 1826 by August Breithaupt from the Greek όλίγος and κλάσις for "little" and fracture alluding to its cleavage.
A variety of Albite

A plagioclase feldspar with an albite : anorthite molar ratio ranging from 90 : 10 to 70 : 30.

Originally described from Danvikstull, Stockholm, Södermanland, Sweden.

Visit gemdat.org for gemological information about Oligoclase.

Classification of Oligoclase

9.FA.35

9 : SILICATES (Germanates)
F : Tektosilicates without zeolitic H2O
A : Tektosilicates without additional non-tetrahedral anions
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Physical Properties of Oligoclase

Vitreous, Sub-Vitreous
Diaphaneity (Transparency):
Transparent, Translucent
Colour:
Colourless, white, very pale yellow
Comment:
may be green due to inclusions
Streak:
White
Hardness (Mohs):
6 - 6½
Tenacity:
Brittle
Cleavage:
Perfect
{001} perfect, {010} good, {110} poor
Fracture:
Irregular/Uneven, Sub-Conchoidal, Step-Like
Comment:
The angles between the good and perfect cleavages are usually 93-94 degrees
Density:
2.63 - 2.66 g/cm3 (Measured)    2.65 g/cm3 (Calculated)

Chemical Properties of Oligoclase

Formula:
(Na,Ca)[Al(Si,Al)Si2O8]
Essential elements:
All elements listed in formula:
Analytical Data:
Refractive Index is related to chemical composition and increase with CaAl substitution: alpha 1.533-1.544, beta 1.537-1.548, gamma 1.542-1.552; birefringence 0.008-0.009

Relationship of Oligoclase to other Species

Member of:
Other Members of Group:
AlbiteNaAlSi3O8
Amazonite
Andesine(Na,Ca)[Al(Si,Al)Si2O8]
AnorthiteCaAl2Si2O8
Anorthoclase(Na,K)AlSi3O8
BanalsiteBaNa2[Al2Si2O8]2
Buddingtonite(NH4)AlSi3O8
Bytownite(Ca,Na)[Al(Al,Si)Si2O8]
CelsianBaAl2Si2O8
DmisteinbergiteCaAl2Si2O8
Hyalophane(K,Ba)[Al(Si,Al)Si2O8]
Labradorite(Ca,Na)[Al(Al,Si)Si2O8]
MicroclineKAlSi3O8
OrthoclaseKAlSi3O8
ParacelsianBaAl2Si2O8
ReedmergneriteNa[BSi3O8]
SanidineKAlSi3O8
Slawsonite(Sr,Ca)Al2Si2O8
StronalsiteSrNa2[Al2Si2O8]2
SvyatoslaviteCaAl2Si2O8
9.FA.05KaliophiliteKAlSiO4
9.FA.05KalsiliteKAlSiO4
9.FA.05Nepheline(Na,K)AlSiO4
9.FA.05Panunzite(K,Na)AlSiO4
9.FA.05Trikalsilite(K,Na)AlSiO4
9.FA.05Yoshiokaite(Ca,Na)[Al(Al,Si)O4]
9.FA.05MegakalsiliteKAlSiO4
9.FA.10MalinkoiteNaBSiO4
9.FA.15VirgiliteLiAlSi2O6
9.FA.25LisitsyniteKBSi2O6
9.FA.30AdulariaKAlSi3O8
9.FA.30Anorthoclase(Na,K)AlSi3O8
9.FA.30Buddingtonite(NH4)AlSi3O8
9.FA.30CelsianBaAl2Si2O8
9.FA.30Hyalophane(K,Ba)[Al(Si,Al)Si2O8]
9.FA.30MicroclineKAlSi3O8
9.FA.30OrthoclaseKAlSi3O8
9.FA.30SanidineKAlSi3O8
9.FA.30Rubicline(Rb,K)AlSi3O8
9.FA.30MonalbiteNaAlSi3O8
9.FA.35AlbiteNaAlSi3O8
9.FA.35Andesine(Na,Ca)[Al(Si,Al)Si2O8]
9.FA.35AnorthiteCaAl2Si2O8
9.FA.35Bytownite(Ca,Na)[Al(Al,Si)Si2O8]
9.FA.35Labradorite(Ca,Na)[Al(Al,Si)Si2O8]
9.FA.35ReedmergneriteNa[BSi3O8]
9.FA.40ParacelsianBaAl2Si2O8
9.FA.45SvyatoslaviteCaAl2Si2O8
9.FA.45KumdykoliteNaAlSi3O8
9.FA.50Slawsonite(Sr,Ca)Al2Si2O8
9.FA.55LisetiteCaNa2Al4Si4O16
9.FA.60BanalsiteBaNa2[Al2Si2O8]2
9.FA.60StronalsiteSrNa2[Al2Si2O8]2
9.FA.65DanburiteCaB2Si2O8
9.FA.65MaleeviteBaB2Si2O8
9.FA.65PekoviteSrB2Si2O8
9.FA.70Lingunite(Na,Ca)AlSi3O8
9.FA.75KokchetaviteKAlSi3O8

Other Names for Oligoclase

Other Information

Not usually fluorescent in SW UV; may be faint red to faint white.
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 Oligoclase

Reference List:
American Mineralogist (1968): 53: 1709-1723.

Zeitschrift für Kristallographie (1971): 133: 43.

Internet Links for Oligoclase

Specimens:
The following Oligoclase specimens are currently listed for sale on minfind.com.

Localities for Oligoclase

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.
Mineral and/or Locality  
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