A cluster of microcline twinned crystals (10,0 x 9,5 cm) By Tom Epaminondas (mineral collector) and Eurico Zimbres (FGEL/UERJ) (Own work) [Public domain], via Wikimedia Commons
Microcline is a variety of feldspar. The only microcline you are likely to encounter is amazonite.
Microcline Value
Highest values go to color, transparency, size.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Microcline Information
| Data | Value |
| Name | Microcline |
| Is a Variety of | Feldspar |
| Varieties | Amazonite |
| Crystallography | Triclinic |
| Refractive Index | 1.518 - 1.534 |
| Colors | White green blue pink orange |
| Polish Luster | Greasy to vitreous |
| Fracture Luster | Pearly to vitreous |
| Fracture | Uneven to splintery |
| Hardness | 6 - 6.5 |
| Toughness | Poor |
| Specific Gravity | 2.54 - 2.58 |
| Cleavage | Perfect and easy in two directions |
| Stone Sizes | Amazonite cabochons up to almost any size are available; the material is usually sold by the pound to hobbyists. The same applies to perthite. The Amelia material has fine color and translucency, but perfect cleavage adds fragility. |
| Heat Sensitivity | Yes |
| Enhancements | Wax impregnation, hides fractures, common, moderately stable, detect with hot point. Irradiation, produces blue amazonite from white microcline, rare, stable, undetectable. |
| Transparency | Semitranslucent to opaque |
| UV Long | Inert to weak yellowish green |
| UV Short | Inert |
| Phenomena | Adventurescence in amazonite |
| Identifying Characteristics | Mottled coloring with grid like patterns |
| Formula | KAlSi3O8 (Note, this is the same formula as orthoclase, but a different crystal system.) |
| Pleochroism | None |
Comments
Microcline crystals, associated with smoky quartz, are popular mineral specimens from the Pike’s Peak area of Colorado. The color of amazonite ranges from pale green to dark green and blue-green. Pinkish orthoclase is also often present as an intergrowth.
Name
Microcline is from Greek words meaning small and inclined because the cleavage is close to but not quite 90°.
FELDSPAR: Micro-amazonite, Amelia Court House Virginia, (1inch); Canada (~2 inches across)
Occurrence
Microcline occurs in acidic alkali-rich plutonic rocks; also in rocks such as pegmatites, granites, syenites, and schists.
- Pala, California; Maine: New York: North Carolina.
- USSR; Norway; Sweden: Germany; Italy; Japan: South Africa.
- Colorado (Pikes Peak area): amazonite.
- Amelia Courthouse. Virginia: finest amazonite in the United States.
- South Dakota: perthite.
- Canada: perthite, especially Ontario and Quebec.
- Brazil: fine amazonite.
- India (Kashmir District): amazonite.
- Australia (Harts Range).
Amazonite
