The plagioclase feldspar bytownite

	Chemical Formula	(Na,Ca)Al_1-2Si_3-2O₈
	Composition	Sodium calcium aluminum silicate. The ratio of sodium to calcium is about 1:9. The amount of aluminum atoms are between 1 and 2, and the amount of silicon atoms are between 3 and 2. In the Plagioclase Feldspar series, Bytownite contains between 10 and 30 percent Albite (Ab), and between 70 and 90 percent Anorthite (An).
	Color	Colorless, white, cream, pale yellow, light green, yellow-brown, brown, pink, gray
	Streak	White
	Hardness	6 - 6½
	Crystal Forms and Aggregates	(Triclinic) Rarely occurs in crystals, which are tabular and usually twinned. Usually occurs massive, grainy, and as compact crystal groupings. Also occurs as blocky crystal fragments.
	Transparency	Transparent to translucent
	Specific Gravity	2.72 - 2.74
	Luster	Vitreous. Pearly on cleavage surfaces.
	Cleavage	2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal The cleavage angle is about 90º
	Fracture	Conchoidal to uneven
	Tenacity	Brittle
	In Group	Silicates ; Tectosilicates ; Feldspar group ; Plagioclase Feldspars
	All About	Bytownite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Albite is one end member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. The intermediary members are Oligoclase, Andesine, Labradorite, and Bytownite. Bytownite is a rarer form of Feldspar, and is usually translucent without a crystal form. However, a very rare occurrence of transparent, straw-yellow crystals, unlike any other Bytownite, was recently discovered.
	Uses	Bytownite is a rare Feldspar and its only real use is as specimens for collectors.
	Striking Features	Crystal habits, localities, and cleavage
	Popularity (1-4)	3
	Prevalence (1-3)	3
	Demand (1-3)	2
	Distinguishing Similar Minerals	There are many minerals that can be confused with Bytownite, but the localities and cleavage can usually distinguish it from all other minerals.
	Commonly Occurs With	Quartz, Muscovite, Biotite, Hornblende
	Noteworthy Localities	Bytownite is a rare mineral, but occurs in many scattered localities. It is named after the locality of Bytown, the old name for Ottawa, the capitol of Canada. It is also found in Crystal Bay, Minnesota.
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