Sunstone
Image: James St. John (CC BY 2.0)
Mineral NameSunstone
Chemical Formula(Na,Ca)(Al,Si)AlSi2O8
Mohs Hardness6
Crystal Systemtriclinic
Lustervitreous
Streak Colorwhite
Cleavageperfect in two directions (pinacoidal), nearly at 90 degrees (86° and 94°)
Fractureuneven
Specific Gravity2.65
Colorsyellow, green, orange, red, colorless, multi-colored
Transparencytransparent
Type LocalitySpectrum Mine, Oregon, USA
Mineral GroupSilicates
Usesjewelry, collector
Associated Mineralspyroxene, olivine, magnetite
Rarityuncommon
Description
A faceted, cushion-cut sunstone gemstone, approximately 1.3 cm across, displaying a light yellowish-greenish body color and internal reflections. It is a transparent plagioclase feldspar with tiny native copper inclusions.
Geological Context
Sunstone forms as plagioclase phenocrysts within Tertiary-aged, porphyritic, mafic volcanic rocks. The characteristic aventurescence is due to inclusions of native copper.
