monoclinic Tectosilicates
Orthoclase (Prismatic)
Formula KAlSi3O8
Crystal Structure
#! Species: Orthoclase (K-Feldspar)
#! System: Monoclinic (2/m)
#! Habit: Prismatic with multiple pinacoids
monoclinic[2/m]:{010}@1.0 + {001}@0.8 + {100}@0.9 + {110}@0.6
monoclinic
2/m
{010} {001} {100} {110}
Quick Facts
Hardness
6.0
Specific Gravity
2.55
Refractive Index
1.518
Optical Character
Biaxial -
Physical Properties
- Crystal System
- monoclinic
- Hardness (Mohs)
- 6.0
- Specific Gravity
- 2.55
- Cleavage
- Perfect {001} and {010} at approximately 90 degrees
- Fracture
- Uneven to conchoidal
- Lustre
- Vitreous to pearly
Optical Properties
- Refractive Index
- 1.518
- Birefringence
- 0.005-0.008
- Optical Character
- Biaxial -
- Dispersion
- 0.012
- Pleochroism
- None to weak
Characteristics
Colours
ColorlessWhiteCreamPinkYellow (noble orthoclase)GrayGreen
Localities
Madagascar (gem quality, moonstone)Italy (Baveno twins)GermanyUSA (various)AustriaWorldwide in granites
Crystal Forms
prismpinacoidBaveno twinsManebach twins
Related Minerals
Other minerals in the monoclinic system
