monoclinic Tectosilicates
Moonstone
Formula KAlSi3O8
Crystal Structure
#! Species: Moonstone (Orthoclase Feldspar)
#! System: Monoclinic (2/m)
#! Habit: Prismatic with adularescence phenomenon
monoclinic[2/m]:{010}@1.0 + {110}@0.8 + {001}@0.7 + {100}@0.5 | phenomenon[adularescence]
monoclinic
2/m
{010} {110} {001} {100}
Quick Facts
Hardness
6.0
Specific Gravity
2.56
Refractive Index
1.518
Optical Character
Biaxial -
Physical Properties
- Crystal System
- monoclinic
- Hardness (Mohs)
- 6.0
- Specific Gravity
- 2.56
- Cleavage
- Perfect in two directions at ~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
- Phenomenon
- Adularescence
- Fluorescence
- Weak bluish-white in some specimens
Characteristics
Colours
Colorless with blue sheenWhite with white sheenGreyPeach with white sheenRainbow (multicoloured flashes)
Localities
Sri LankaIndiaMyanmarTanzaniaMadagascarAustralia
Common Inclusions
Centipede inclusionsStress cracks from cleavageExsolution lamellae (cause of phenomenon)
Known Treatments
Generally not treatedSurface coating (rare, to enhance sheen)
Crystal Forms
prismpinacoid
Related Minerals
Other minerals in the monoclinic system
