triclinic Tectosilicates
Plagioclase (Albite Twin)
Formula (Na,Ca)(Al,Si)4O8
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}
Quick Facts
Hardness
6.0
Specific Gravity
2.62
Refractive Index
1.525
Optical Character
Biaxial + or -
Physical Properties
- Crystal System
- triclinic
- Hardness (Mohs)
- 6.0
- Specific Gravity
- 2.62
- Cleavage
- Perfect in two directions at approximately 90 degrees
- Fracture
- Uneven to conchoidal
- Lustre
- Vitreous to pearly
- Twin Law
- Albite Law (polysynthetic)
Optical Properties
- Refractive Index
- 1.525
- Birefringence
- 0.007-0.013
- Optical Character
- Biaxial + or -
- Dispersion
- 0.012
- Pleochroism
- None to weak
Characteristics
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
Related Minerals
Other minerals in the triclinic system
