About
In some mineral reference guides, Microcline and Sanidine are wrongly categorized as variety of Orthoclase. Since it is so difficult to distinguish between Orthoclase, Sanidine, and Microcline, they may be simply called "Potassium Feldspar".
Microcline sometimes forms in association with Albite or other Plagioclase feldspar in alternating patterns, and forms a feldspar rock known as Perthite.
Crystal Forms & Aggregates
Click here for more detailed information on the crystal structure of the Feldspars.
Complex Tests
Striking Features
Environment
Varieties
✓ common · ✗ uncommon
- Amazonite— Deep green or greenish-blue variety of Microcline. Also called Amazonstone or Amazon Stone.
See the gemstone section on Amazonite for more information. - Sunstone— Form of orange feldspar that has inclusions of Hematite (or in one locality Copper) that give it a glittering effect. Depending on the locality, Sunstone may be Microcline feldspar, or it may be the Plagioclase feldspar Oligoclase.
Polymorphs
Uses
Also see the gemstone section on Amazonite.
Noteworthy Localities
Large crystals once came from Bedford, Westchester Co., New York; Leiper's Quarry, Delaware Co., Pennsylvania; the Poor House Quarry, West Bradford, Chester Co., Pennsylvania; Middletown, Middlesex Co., Connecticut; and Moat Mountain, Carroll County, New Hampshire. White to light pink Microcline has come from the French Creek area, Chester Co., Pennsylvania. Well formed crystals are widespread at Mont Saint Hilaire, Quebec, Canada.
The variety Amazonite provides many outstanding localities. Deep green Amazonite has come from Parusnaya Mountain, Kola Peninsula, Russia; Santa Maria de Itabira, Minas Gerais, Brazil; Mogok, Burma (Myanmar); and Kenticha and Konso, Sidamo-Borana Province, Ethiopia.
Some of the finest material is from the Pikes Peak area in Colorado. This region encompasses a large area in El Paso, Teller, Douglas, and Park counties. Particularly exceptional deposits in this area include Pikes Peak, Crystal Peak, Devils Head, Lake George, and Florissant. Although some of the deposits are quite distant from each other, all material from this area may be referred to as "Pikes Peak Amazonite", as all the material from this area is almost identical.
Other U.S. occurrences of Amazonite are Amelia Court House, Amelia Co., Virginia; the Zapot pegmatite, Mineral Co., Nevada; Fairfield, Utah Co., Utah; Valhalla, Westchester Co., New York; and Franklin, Sussex Co., New Jersey.
The Sunstone form of Microcline comes Oregon at the Dust Devil Mine, Plush, Lake Co., and from the Ponderosa Sunstones Mine, Harney Co., where it has Copper inclusions.
Common Mineral Associations
Distinguishing Similar Minerals
Sanidine - Indistinguishable without complex methods. Sanidine, however, is never opaque.
Plagioclase Feldspar - May exhibit striations on twinned crystal surfaces, otherwise difficult to distinguish.
Spodumene - Has a splintery fracture.
Calcite - Much lower hardness.
Photos
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