Satin Spar (often marketed as Selenite)
Gypsum var. Satin Spar · Mineral Specimen / Decorative Stone
Crystal System
Monoclinic; typically exhibits a fibrous, prismatic, or columnar habit in this variety.
Mineral Group
Sulfates; Hydrated calcium sulfate.
Chemical Formula
CaSO4·2H2O (Calcium Sulfate Dihydrate)
Formation Process
Sedimentary; forms through the evaporation of mineral-rich saltwater in basins or through hydrothermal activity in caves.
About This Crystal
A translucent to opaque white fibrous material with a distinct pearly to silky luster. It appears as a parallel bundle of fine fibers that catch the light.
Physical Characteristics
White color, white streak, perfect cleavage in one direction (though fibrous), splintery fracture, specific gravity of 2.3, non-magnetic, sometimes fluorescent.
Optical Properties
Biaxial positive; shows a strong silky chatoyancy (cat's eye effect) due to the parallel fibrous structure reflecting light.
Hardness & Durability
Origin Region
Morocco (most common), Mexico (Naica), USA, and Brazil; found in evaporite sedimentary environments.
Hardness & Durability
Mohs hardness of 2; extremely soft (can be scratched by a fingernail). Brittle and fragile; not suitable for faceted jewelry.
Care & Maintenance
Keep dry; soluble in water over time. Do not use ultrasonic or steam cleaners. Clean with a soft, dry cloth. Store away from harder stones to prevent scratching.
Rarity & Value
Very common; inexpensive. Value is based on size and the absence of brown/red iron staining. Rarely treated, though sometimes dyed.
Special Characteristics
Fibrous chatoyancy produces a 'glow' or 'shimmer' when rotated. It is a natural fiber-optic material.
Lore & History
Named after the Greek word 'selēnitēs' meaning moon-stone. Historically used for window panes in ancient Rome. In metaphysical lore, it is used for mental clarity and cleansing.