Plagioclase Mineral Data

Plagioclase Mineral Data +

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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.

Plagioclase Image

Images:

Plagioclase Albite

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:

Plagioclase Albite

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

Images:

Plagioclase Labradorite

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 the 010 polysynthetic twinning planes (Albite Law).
Location: Ihosy, Betroka district, Toliara Province, Madagascar. Scale: Picture size 3x3 cm.
© Dave Barthelmy

Images:

Plagioclase Oligoclase

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

Images:

Plagioclase Anorthite

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:

Plagioclase Andesine

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

Images:

Plagioclase Bytownite

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

Images:

Plagioclase Oligoclase

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 - PinacoidalH-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

Diaphaniety:

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:

r_electron=2.67 gm/cc
note: r_Plagioclase=2.69 gm/cc.

Fermion Index

Fermion Index = 0.01485
Boson Index = 0.98515

Photoelectric:

PE_Plagioclase= 2.46 barns/electron
U=PE_Plagioclase x r_electron= 6.56 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Plagioclase is Not Radioactive

Plagioclase Classification

Dana Class:

76.1.3.0 (76)Tectosilicate Al-Si Framework

(76.1)with Al-Si frameworks

(76.1.3)Plagioclase series

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

76.1.3.1 Albite NaAlSi3O8 C1 1

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

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

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

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

76.1.3.6 Anorthite CaAl2Si2O8 P1,I1 1

Strunz Class:

VIII/J.07-00 VIII - Silicates

VIII/J - Tectosilicates (network) without anions unfamiliar to the tetraheders

VIII/J.07 - Feldspar group, Anorthoclase - Anorthite - Banalcite series

Other Plagioclase Information

References:

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

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Plagioclase

(Na,Ca)(Si,Al)4O8
Dana No: 76.1.3.0 Strunz No: VIII/J.07-00
Locality:

Notes: