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Celsian is a very rare barium-rich member of the feldspar group. This mineral is named after Anders Celsius (1701-1744), a famous Swedish astronomer and scientist who proposed the Celsius temperature scale. Celsian forms a solid solution series with Orthoclase, and the intermediary member is known as Hyalophane. Although sometimes viewed as a variety of Celsian, Hyalophane is scientifically classified as a distinct mineral species. |
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Chemical Formula |
BaAl2Si2O8 |
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Composition |
Barium aluminum silicate, sometimes with some calcium and potassium.
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| Variable Formula |
(Ba,Ca,K)Al2Si2O8 |
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Color |
Colorless, white, light yellow, brown, reddish-brown, blue, gray |
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Streak |
White |
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Hardness |
6 - 6.5 |
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Crystal System |
Monoclinic |
Crystal Forms
and Aggregates |
Occurs as short tabular crystals and as long, slender prisms. Also occurs acicular, massive, and as crusts.
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Transparency |
Transparent to opaque |
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Specific Gravity |
3.1 - 3.4 |
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Luster |
Vitreous to greasy |
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Cleavage |
2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal. The cleavage angle is about 90º. |
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Fracture |
Conchoidal to uneven |
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Tenacity |
Brittle |
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Complex Tests |
Soluble in hydrochloric acid |
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In Group |
Silicates; Tectosilicates; Feldspar Group |
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Striking Features |
Heaviness and localities |
| Environment |
In barium-rich contact metamorphic rocks.
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| Rock Type |
Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
3 |
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- Intermediary member of the Celsian-Orthoclase mineral series. Although sometimes
viewed as a variety of Celsian, Hyalophane is scientifically classified as a distinct
mineral species.
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Celsian is a very rare mineral. Localities include the Benallt Mine, Rhiw, Wales; Jakobsberg, Nordmark, Sweden; Candoglia, Piedmont, Italy; the Kaso Mine, Kanuma, Japan; Broken Hill, New South Wales, Australia; and Franklin, Sussex Co., New Jersey. Hyalophane localities are the Zagradski Potok Mine, Busovaca, Bosnia and Herzegovina; and the Lengenbach Quarry, Im Feld, Binntal, Switzerland.
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Other Feldspars - Considerably lighter in weight.
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