About Microcline
KAlSi₃O₈
The triclinic, low-temperature potassium feldspar and a main component of granites and pegmatites. Its green to blue-green variety amazonite is a classic collector mineral; the cause of that colour is still debated, with lead plus structural water as the leading explanation and Rb, Tl or Fe2+ also proposed.
Photos of Microcline
Long white microcline crystal with a glassy overgrowth rim on matrix, Hashupa, Shigar Valley.
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Intensely turquoise amazonite crystal from the Kenticha mine.
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Two large intergrown amazonite crystals with deep blue-green colour, Konso.
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Large white-capped blue-green amazonite crystal, Florissant (Topaz Butte).
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Stepped Manebach-twinned turquoise amazonite crystal, Smoky Hawk claim.
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Deep blue-green amazonite crystal from the Take 5 claim, Crystal Peak area.
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Microcline specimen from Papachacra, Catamarca (photo by its collector).
Photo: Leon Hupperichs · CC BY-SA 3.0 · Source
Intergrown turquoise amazonite crystals with two smoky quartz crystals, Kosnar claim, Lake George.
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Where Microcline is found (15)
Argentina
- PapachacraCatamarca · 5 photos
Australia
- Broken Hill Pb-Zn-Ag depositNew South Wales · 1 photo
Ethiopia
- Kenticha mineOromia · 5 photos
- KonsoSouth Ethiopia Regional State · 5 photos
Japan
- TanakamiyamaShiga Prefecture · 1 photo
Myanmar
- MogokMandalay Region · 1 photo
Namibia
- Erongo MountainErongo · 2 photos
Pakistan
- Shigar ValleySkardu District · 5 photos
United States
- Crystal Peak (Teller County)Colorado · 5 photos
- Florissant area (Teller County)Colorado · 5 photos
- Himalaya MineCalifornia · 3 photos
- Lake George (Park County)Colorado · 5 photos
- Pikes PeakColorado · 5 photos
- Rincon Pegmatite DistrictCalifornia · 1 photo
- Smoky Hawk claimColorado · 5 photos
Microcline on the same specimen with other minerals
1 specimen photo(s) from this locality show quartz with microcline together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show quartz with microcline together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show quartz with microcline together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with albite together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
2 specimen photo(s) from this locality show microcline with albite together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with albite together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
2 specimen photo(s) from this locality show microcline with albite together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with fluorite together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
2 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with albite together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
2 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with quartz together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
1 specimen photo(s) from this locality show microcline with fluorite together. The pairing comes from the photographer's file name and label, so the relationship between the two minerals is not specified.
Identity
- Also called
- Amazonite (green to blue-green variety); amazonstone
- Group
- Feldspar Group
- Strunz
- 9.FA.30 · 9 Silicates
- IMA status
- Grandfathered
- Name origin
- From Greek words for 'little' and 'inclined', because the cleavage angle departs slightly from 90°.
- Elements
- K, Al, Si, O
Physical properties
- Color
- White, pale cream-yellow, salmon-red, green to blue-green (amazonite) or blue; colourless in thin section
- Luster
- Vitreous luster
- Transparency
- Variable
- Mohs hardness
- 6–6.5
- Density
- 2.54–2.57 g/cm³
- Cleavage / fracture
- Perfect cleavage on {001} and {010}, meeting at about 90°; partings on {100}, {110}, {1-10} and {-201}; fracture uneven; brittle
- Magnetism / fluorescence
- Some specimens fluoresce red in shortwave UV
Crystallography
- Crystal system
- Triclinic
- Space group
- C-1
- Structure
- Feldspar framework of linked SiO4 and AlO4 tetrahedra with K in the cavities; Si and Al are fully ordered in low microcline. Dimorphous with monoclinic orthoclase.
- Typical habit
- Prismatic crystals elongated along [001] or [100], possibly the largest crystals of any species (to 50 m); cleavable to granular masses; commonly perthitic with exsolved albite lamellae
- Twinning
- Carlsbad, Baveno and Manebach twins very common; combined albite- and pericline-law polysynthetic twinning gives a cross-hatched grid on (001)
- Optical data
- Biaxial (-); nα = 1.514-1.529, nβ = 1.518-1.533, nγ = 1.521-1.539; 2V 66-103°; weak dispersion r > v
Formation and use
- Formation
- Common in felsic plutonic rocks (granites, granite pegmatites, syenites), in greenschist- and amphibolite-facies metamorphic rocks and in hydrothermal veins; detrital and as authigenic overgrowths in sedimentary rocks.
Related minerals
- Related minerals
- Albite
- Polymorphs
- Orthoclase
Sources
- SRC-560 · Book
Handbook of Mineralogy - MicroclineAnthony, J.W.; Bideaux, R.A.; Bladh, K.W.; Nichols, M.C. · 2001 · Mineral Data Publishing / Mineralogical Society of America - SRC-561 · Database
Microcline Mineral DataBarthelmy, D. · Webmineral.com - SRC-562 · Website
AmazoniteWikipedia contributors · Wikipedia
Draft data from the Provenite workbook. Check entries against the cited sources before relying on them. Photos are open-licence images from Wikimedia Commons; the author and licence are given with each photo.