Strontium Feldspar
Strontium aluminosilicate (SrAl2Si2O8)
Feldspar in which strontium dominates the large cation site, represented mainly by the rare mineral slawsonite.
- Mohs hardness
- 6
- Color
- Colorless to white
- Type
- mineral
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Overview
Strontium feldspar denotes feldspar-group minerals in which strontium (Sr) is the dominant large cation, the principal natural species being slawsonite (SrAl2Si2O8). Strontium can also substitute partially into calcium and barium feldspars.
Because strontium is rarely concentrated enough in rocks to dominate a feldspar, strontium feldspar is very rare and occurs as small colorless to white grains.
It is essentially a research and collector mineral, important for understanding how strontium partitions into silicate frameworks during metamorphism.
Formation & geology
Strontium feldspar forms in strontium-enriched metamorphic and hydrothermally altered rocks, including metamorphosed manganese deposits and rocks derived from celestine- or strontium-rich protoliths.
When these rocks recrystallize, strontium can be incorporated into the feldspar structure to form slawsonite, often alongside barium minerals such as celsian and paracelsian, with which strontium feldspar is chemically related.
Reported occurrences include the Wallowa Mountains of Oregon, USA, and metamorphic manganese deposits in Japan, where Sr-Ba mineral assemblages develop.
How to identify it
Strontium feldspar is colorless to white with a vitreous luster, white streak, and Mohs hardness around 6, indistinguishable by eye from other feldspars.
Its strontium dominance is detectable only with chemical analysis (electron microprobe) or X-ray diffraction. Slightly elevated density relative to common feldspar and an association with strontium/barium minerals are weak contextual clues.
It is most likely to be confused with barium feldspars (celsian, paracelsian) and ordinary plagioclase; only laboratory work resolves the difference.
Uses & significance
Strontium feldspar has no industrial or gem use. It is too rare and fine-grained to mine, and strontium for industry is obtained from celestine and strontianite instead.
Its significance is purely scientific, as an indicator of strontium enrichment and as a member of the Sr-Ba feldspar family that helps mineralogists study cation substitution in framework silicates.
Good specimens are sought by systematic mineral collectors.
Frequently asked questions
What is the main strontium feldspar mineral?
Slawsonite, SrAl2Si2O8, is the principal strontium-dominant feldspar species.
Why is strontium feldspar so rare?
Strontium seldom becomes concentrated enough in rocks to dominate over calcium, sodium, potassium, or barium in feldspar.
Where is strontium feldspar found?
In strontium-rich metamorphic and manganese deposits, including localities in Oregon, USA, and Japan.
Is strontium feldspar used commercially?
No. Strontium ore comes from celestine and strontianite, and strontium feldspar has no practical use.
Strontium Feldspar guides
In-depth guides for identifying, valuing, and understanding Strontium Feldspar.
