Sunstone
Plagioclase Feldspar (var. Sunstone/Oligoclase) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Triclinic; typically occurs in massive, granular, or blocky habits
Mineral Group
Silicates (Tectosilicate), Feldspar Group, Plagioclase Series
Chemical Formula
(Na,Ca)(Al,Si)4O8 with trace Copper or Hematite (Fe2O3)
Formation Process
Igneous: Crystallizes within cooling magma, often as part of basaltic flows or granitic pegmatites, where exsolution of trace minerals creates the aventurescence effect
About This Crystal
The specimen shows a mixture of peach, orange, and white feldspar. It exhibits a blocky to granular habit with a vitreous to pearly luster. The transparency ranges from translucent to opaque, with visible darker inclusions and scattering metallic glitters
Physical Characteristics
Color: Orange, peach, white; Streak: White; Cleavage: Perfect in two directions at nearly 90 degrees; Fracture: Conchoidal to uneven; Specific Gravity: 2.62-2.65; Tenacity: Brittle; Fluorescence: Often weak reddish-orange
Optical Properties
Biaxial (+/-), Refractive Index: 1.532-1.552, Birefringence: 0.007–0.010. Exhibits Aventurescence (schiller effect) due to light reflecting off copper or hematite platelets
Hardness & Durability
Origin Region
Oregon (USA), Norway, Tanzania, Madagascar, and India; typically found in igneous rocks such as basalt or pegmatites
Hardness & Durability
Mohs Hardness: 6.0 - 6.5; Toughness: Poor due to perfect cleavage; Wearability: Fair (requires protective settings in jewelry)
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic cleaners and steam cleaners. Store away from harder gems like sapphires or diamonds to prevent scratching
Rarity & Value
Relatively common; value is determined by the intensity of the aventurescence (schiller), clarity, and size. Oregon Sunstone with high copper content is the most prized
Special Characteristics
Displays Aventurescence (a metallic glittery effect caused by inclusions) and can occasionally show pleochroism or labradorescence depending on the specific feldspar mix
Lore & History
Historically used by Vikings for navigation (as a 'Sunstone' polarized light filter, though debated). Traditionally associated with the Solar Plexus chakra, leadership, and personal power