The feldspar microcline

	Chemical Formula	KAlSi₃O₈
	Composition	Potassium aluminum silicate.
	Color	White, cream, light yellow, light brown, reddish-brown, pink, blue-green, deep green
	Streak	White
	Hardness	6
	Crystal Forms and Aggregates	(Triclinic) Occurs in well formed crystals, which may be enormous in size. The crystals of Microcline are very similar to those of Orthoclase, and form the same twins. Microcline also occurs in grainy and in compact crystal aggregates. Crystals are frequently striated.
	Transparency	Translucent to opaque
	Specific Gravity	2.5 - 2.6
	Luster	Vitreous
	Cleavage	2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal The cleavage angle is about 90º
	Fracture	Conchoidal to uneven
	Tenacity	Brittle
	Varieties	Amazonite or Amazonstone - Deep green or greenish-blue variety Myrmekite - Intergrowth of Microcline and Quartz See also Perthite
	Polymorphs	Orthoclase, Sanidine
	In Group	Silicates ; Tectosilicates ; Feldspar group ; Potassium feldspars
	All About	Microcline is polymorphous with Orthoclase and Sanidine. These three minerals form the Potassium Feldspar group. They are almost identical in physical properties, and sometimes it is impossible to distinguish one another without x-ray analysis. The only difference between them is their crystal structure. Microcline crystallizes in the triclinic system, and Orthoclase and Sanidine crystallize in the monoclinic system. Sanidine forms at high temperatures and has a disordered monoclinic symmetry, whereas Orthoclase forms at low temperatures and cools slowly, forming more ordered monoclinic crystals. [For more information on the crystal structure of the feldspars, see "All about" in the mineral Anorthite] In many 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". Crystals of Microcline are generally much larger than those of Orthoclase, and deep green is a sure sign of Microcline, since Orthoclase does not exist in deep green examples.
	Uses	Microcline is important in the manufacture of glass and ceramics. Crystals and twins are studied by scientists, as they provide information on the formation of minerals and environmental factors. Well shaped crystals and twins, and crystals of green "Amazonite" are highly sought after by mineral collectors. The variety Amazonite is an important gem. It is cut into beads and cabochons, and is carved into ornamental figures.
	Striking Features	Crystal habits, cleavage, and hardness
	Complex Tests	Soluble in hydrofluoric acid
	Popularity (1-4)	2
	Prevalence (1-3)	1
	Demand (1-3)	2
	Distinguishing Similar Minerals	Orthoclase - Indistinguishable without complex methods. However, Microcline can have a deep green color that Orthoclase cannot achieve. Sanidine - Indistinguishable without complex methods. Sanidine, however, is never opaque. Plagioclase feldspars - exhibits striations on twinned crystal surfaces Spodumene - has a splintery cleavage Calcite - much softer (3)
	Commonly Occurs With	Quartz, Muscovite, Plagioclase feldspars
	Noteworthy Localities	Microcline is a very common mineral, and is found worldwide. Enormous white crystals were once abundant at Bedford, Westchester Co., New York; Leiper's Quarry, Delaware Co., Pennsylvania, and at Middletown, Middlesex Co., Connecticut. Well formed crystals are widespread at Mont Saint Hilaire, Quebec (Canada). White to light pink Microcline has come from the French Creek area, St. Peters, Chester Co., Pennsylvania. The variety Amazonite comes from several areas in Brazil, India, Madagascar, and Russia. Some of the finest material is from the Pikes Peak area in Colorado. This region encompasses a large area in El Paso, Teller, and Douglas counties. Particularly exceptional deposits in this area include Pikes Peak, Crystal Peak, and Devils Head. Although some of the deposits are quite distant from each other, all material from this area is usually called "Pikes Peak Amazonite", as all the material from this area is identical. Amazonite with beautiful coloring comes from Amelia Court House, Amelia Co., Virginia, although it lacks the crystalline form of the Colorado type. Two other Amazonite localities are Fairfield, Utah Co., Utah, and Mineral Hill, Media, Delaware Co. Pennsylvania.
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