Plagioclase Mineral Data

General Plagioclase Information

Chemical Formula:

(Na,Ca)(Si,Al)4O8

Composition:

Molecular Weight = 270.77 gm

Sodium 4.25 % Na 5.72 % Na₂O

Calcium 7.40 % Ca 10.36 % CaO

Aluminum 9.96 % Al 18.83 % Al₂O₃

Silicon 31.12 % Si 66.57 % SiO₂

Oxygen 47.27 % O

______ ______

100.00 % 101.48 % = TOTAL OXIDE

Empirical Formula:

Na_0.5Ca_0.5Si₃AlO₈

Environment:

Igneous and metamorphic rocks. Group name for Na, Ca feldspars.

IMA Status:

Not Approved IMA

Locality:

Common world wide occurrences. Link to MinDat.org Location Data.

Name Origin:

From the Greek plagios - "oblique" and klao - "I cleave" in allusion to the obtuse cleavage angles of the good cleavages.

Name Pronunciation:

Plagioclase + Pronunciation

Plagioclase Image

Images:

Albite Plagioclase

Comments: Colorless, lustrous blocky albite crystals to 3 cm in size with a thick dusting of micaceous green micro chlorite.
Location: Acushnet Quarry, Bristol Co., Massachussetts, USA. Scale: 17 x 15 x 7.5 cm matrix.
© Dan Weinrich

Images:

Albite Plagioclase

Comments: Crystal group of bladed albite (variety cleavelandite) crystals.
Location: Taquaral, Minas Gerais, Brazil. Scale: 7.4 x 5 cm.
© John Veevaert

Images:

Labradorite Plagioclase

Comments: Dual view of a cleavage fragment of labradorite showing the multi-colored labradorescence (schiller effect) and the same area viewed without the color. The color is due to optical interference on Bøggild exsolution lamellae.
Location: Ihosy, Betroka district, Toliara Province, Madagascar. Scale: Picture size 3x3 cm.
© Dave Barthelmy

Images:

Oligoclase Plagioclase

Comments: Rectangular cleavage fragment of salmon-orange oligoclase (sunstone) feldspar.
Location: Norway. Scale: 47x30x7 mm.
© John Betts - Fine Minerals

Images:

Anorthite Plagioclase

Comments: Opaque white crystal of anorthite with dark brown solidified lava coating.
Location: Miyake-jima, Shizuoka, Japan. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Images:

Andesine Plagioclase

Comments: Translucent andesine crystal twin.
Location: Maeyama Ueda shi, Nagano, Japan. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Images:

Bytownite Plagioclase

Comments: Translucent crystalline bytownite.
Location: Crystal Bay, Hennepin County, Minnesota, USA. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Images:

Oligoclase Plagioclase

Comments: Clear glassy crystalline oligoclase with milky quartz and muscovite.
Location: Bakersville, Mitchell County, North Carolina, USA. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Images:

Plagioclase

Comments: Plagioclase, variety kenyite, crystals in volcanic rock.
Location: Kirinyaga (Mount Kenya), Central Province, Kenya. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Plagioclase Crystallography

Crystal System:

Triclinic - Pinacoidal H-M Symbol ( 1) Space Group: C1

Physical Properties of Plagioclase

Cleavage:

{001} Good, {010} Good

Color:

White, Gray, Bluish white, Reddish white, Greenish white.

Density:

2.61 - 2.76, Average = 2.68

Diaphaneity:

Transparent to translucent

Fracture:

Brittle - Generally displayed by glasses and most non-metallic minerals.

Habit:

Massive - Granular - Common texture observed in granite and other igneous rock.

Hardness:

6-6.5 - Orthoclase-Pyrite

Luminescence:

Non-fluorescent.

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Plagioclase

Optical Data:

NCalc= 1.56 - from Gladstone-Dale relationship (KC = 0.2101) where Ncalc=Dmeas*KC+1

Calculated Properties of Plagioclase

Electron Density:

Bulk Density (Electron Density)=2.67 gm/cc
note: Specific Gravity of Plagioclase =2.69 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Plagioclase= 2.46 barns/electron
U=PE_Plagioclase x rElectron Density= 6.56 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Plagioclase is Not Radioactive

Plagioclase Classification

Dana Class:

76.01.03.00 (76)Tectosilicate Al-Si Framework

(76.01)with Al-Si frameworks

(76.01.03)Plagioclase series

76.01.03.00 Plagioclase* (Na,Ca)(Si,Al)4O8 C1 1

76.01.03.01 Albite NaAlSi3O8 C1 1

76.01.03.02 Oligoclase (Na,Ca)(Si,Al)4O8 C1 1

76.01.03.03 Andesine* (Na,Ca)(Si,Al)4O8 C1 1

76.01.03.04 Labradorite* (Ca,Na)(Si,Al)4O8 C1 1

76.01.03.05 Bytownite* (Ca,Na)(Si,Al)4O8 C1 1

76.01.03.06 Anorthite CaAl2Si2O8 P1,I1 1

Strunz Class:

09.FA.35 09 - SILICATES (Germanates)

09.F - Tektosilicates without Zeolitic H2O

09.FA -Tektosilicates without additional non-tetrahedral anions, (Al,B):Si = 1:1

09.FA.35 Albite NaAlSi3O8 C1 1

09.FA.35 Bytownite* (Ca,Na)(Si,Al)4O8 C1 1

09.FA.35 Anorthite CaAl2Si2O8 P1,I1 1

09.FA.35 Andesine* (Na,Ca)(Si,Al)4O8 C1 1

09.FA.35 Labradorite* (Ca,Na)(Si,Al)4O8 C1 1

09.FA.35 Oligoclase (Na,Ca)(Si,Al)4O8 C1 1

09.FA.35 Reedmergnerite NaBSi3O8 C1 1

09.FA.35 Plagioclase* (Na,Ca)(Si,Al)4O8 C1 1

Other Plagioclase Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Duda&Rejl90)

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Plagioclase

(Na,Ca)(Si,Al)4O8
Dana No: 76.01.03.00 Strunz No: 09.FA.35
Locality:

Notes:

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