monoclinic Tectosilicates
Orthoclase (Carlsbad Twin)
Formula KAlSi3O8
Crystal Structure
#! Species: Orthoclase (K-Feldspar)
#! System: Monoclinic (2/m)
#! Habit: Carlsbad penetration twin
monoclinic[2/m]:{010}@1.0 + {100}@0.95 + {001}@0.7 + {110}@0.4 | twin(carlsbad)
monoclinic
2/m
{010} {100} {001} {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
prismpinacoidtwin
Related Minerals
Other minerals in the monoclinic system
