triclinic Tectosilicates
Plagioclase (Albite Twin)
(Na,Ca)(Al,Si)4O8
Quick Facts
Hardness
6.0
Specific Gravity
2.62
Refractive Index
1.525
Optical Character
Biaxial + or -
Crystal Structure
#! Species: Plagioclase (Albite)
#! System: Triclinic (-1)
#! Habit: Tabular with polysynthetic albite twinning
triclinic[-1]:{010}@1.0 + {001}@0.8 + {100}@0.5 + {110}@0.4 | twin(albite)
triclinic
-1
{010} {001} {100} {110}
Physical Properties
Crystal Systemtriclinic
Hardness (Mohs)6.0
Specific Gravity2.62
CleavagePerfect in two directions at approximately 90 degrees
FractureUneven to conchoidal
LustreVitreous to pearly
Twin LawAlbite Law (polysynthetic)
Optical Properties
Refractive Index1.525
Birefringence0.007-0.013
Optical CharacterBiaxial + or -
Dispersion0.012
PleochroismNone to weak
Colours
ColorlessWhiteGrayGreenish
Localities
Worldwide occurrence in igneous and metamorphic rocksItalyBrazilMadagascarNorway
Crystal Forms
pinacoidprismtwin
Notes
Albite twinning striations visible on {010} cleavage distinguish plagioclase from orthoclase
Interactive Preview
Open this crystal in the CDL Playground to rotate, export, and explore in 3D.
Open in Playground #! Species: Plagioclase (Albite)
#! System: Triclinic (-1)
#! Habit: Tabular with polysynthetic albite twinning
triclinic[-1]:{010}@1.0 + {001}@0.8 + {100}@0.5 + {110}@0.4 | twin(albite)
Related Minerals
Other minerals in the triclinic system
