Satin Spar (often commercially called Selenite)
Gypsum var. Satin Spar · Decorative Stone / Mineral Specimen
Crystal System
Monoclinic; typically occurs in fibrous, parallel aggregates that create the silky luster.
Mineral Group
Sulfates
Chemical Formula
CaSO4·2H2O (Calcium Sulfate Dihydrate)
Formation Process
Sedimentary; typically forms as an evaporite mineral in saline lakes, lagoons, and clay beds through the evaporation of calcium sulfate-rich water.
About This Crystal
A fibrous variety of gypsum with a pearly or silky luster. This specific specimen is carved into a five-pointed star. It is translucent to nearly transparent along the fibers, exhibiting a white to pale light-gray color with a prominent cat's eye-like sheen.
Physical Characteristics
Color: White/Colorless; Streak: White; Cleavage: Perfect in one direction (though fibrous nature dominates); Fracture: Splintery; Specific Gravity: 2.3; Fluorescence: Can show weak blue or yellow under Long Wave UV.
Optical Properties
Biaxially positive; Refractive Index: 1.520–1.530; exhibiting strong chatoyancy (cat's eye effect) due to the parallel alignment of its internal fibrous structure.
Hardness & Durability
Origin Region
Morocco (most common source for this material), Mexico, USA, and various global evaporite deposits.
Hardness & Durability
Mohs Hardness: 2; extremely soft and can be scratched by a fingernail. Low toughness; fragile and prone to bruising or splintering.
Care & Maintenance
Extremely sensitive; do not soak in water as it can dissolve or lose luster over time. Clean only with a dry, soft cloth. Store separately from harder stones to prevent scratching.
Rarity & Value
Very Common; largely inexpensive and widely available. Value is based primarily on the quality of the carving and the strength of the chatoyant 'flash'.
Special Characteristics
Notable for its strong 'fiber-optic' effect, where light travels along the length of the crystals, creating a moving band of light similar to a cat's eye gemstone.
Lore & History
Historically used for decorative plaster (Plaster of Paris). In modern metaphysical practices, it is associated with the Crown Chakra and believed to be a 'cleansing' stone that dispels negative energy, though these are non-scientific claims.