Barium Feldspar
Barium aluminosilicate (BaAl2Si2O8), celsian
The barium end-member of the feldspar group, represented by celsian, occurring in barium-rich metamorphic and manganese deposits.
- Mohs hardness
- 6-6.5
- Color
- Colorless, white, to pale yellow
- Type
- mineral
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Overview
Barium feldspar refers to feldspars in which barium dominates the large cation site, the principal species being celsian (BaAl2Si2O8). It forms a solid-solution series with potassium feldspar; the intermediate, barium-bearing member is called hyalophane.
Celsian is monoclinic and forms colorless, white, or pale yellow crystals and masses. It is uncommon because barium is rarely concentrated enough in geological systems to make a feldspar.
Barium feldspars are mainly significant to mineralogists, petrologists, and collectors rather than to industry, and they serve as markers of unusual barium-rich conditions.
Formation & geology
Barium feldspar (celsian) forms in barium-enriched metamorphic rocks, especially metamorphosed manganese ore deposits and baryte-bearing sediments subjected to regional or contact metamorphism.
Barium is typically inherited from baryte in the protolith. During metamorphism and hydrothermal alteration, the barium is incorporated into the feldspar framework, producing celsian or, with intermediate barium contents, hyalophane.
Classic occurrences include the Benallt manganese mine in Wales, Jakobsberg and Langban in Sweden, and barium-rich metamorphic rocks elsewhere, where celsian accompanies baryte and manganese silicates.
How to identify it
Barium feldspar is colorless to white or pale yellow, with a vitreous luster, white streak, and Mohs hardness near 6-6.5. It shows the two good cleavages typical of feldspars.
It is hard to separate visually from ordinary feldspars; high specific gravity (celsian is denser than common feldspar because of barium) and an association with barium and manganese minerals are useful clues.
Confirming barium content and distinguishing celsian from its polymorph paracelsian requires X-ray diffraction or chemical analysis.
Uses & significance
Barium feldspar has limited practical use. Celsian is occasionally of interest because barium feldspar compositions have favorable high-temperature and dielectric properties, and synthetic celsian is studied for ceramics.
Natural barium feldspar is too rare to serve as a barium ore (baryte fills that role) and is not used as a gemstone.
Its main value is scientific and as a collector mineral that records barium-rich geological environments.
Frequently asked questions
What mineral is barium feldspar?
It is chiefly celsian, BaAl2Si2O8, the barium end-member of the feldspar group; barium-bearing intermediates are called hyalophane.
Is barium feldspar common?
No. Barium rarely concentrates enough to form feldspar, so it is restricted to barium-rich metamorphic and manganese deposits.
How can you tell celsian from ordinary feldspar?
Celsian has higher density due to barium and occurs with barium minerals, but chemical or X-ray analysis is needed for certainty.
Is barium feldspar used industrially?
Natural celsian is too rare to mine, but synthetic celsian ceramics are studied for their heat-resistant and dielectric properties.
Barium Feldspar guides
In-depth guides for identifying, valuing, and understanding Barium Feldspar.
