Sometimes also known as aventurine feldspar, it owes its attractiveness to the inclusions of red, orange and occasionally green thin platy crystals of goethite or hematite which are disseminated in parallel orientation through the near colorless matrix. The inclusions give the mineral a rich reddish-brown color with spectacular colorful reflections.
Plagioclase (Na-Ca feldspar: albite, oligoclase, andesine,
labradorite,bytownite, anorthite) are part of an isomorphous series, and our sunstone is somewhere in the oligoclase area, i.e. with more Na than Ca).
A new kind of sunset colored labradorite has recently been discovered purportedly from China. Chemically, it falls between labradorite and andesine in the plagioclase series. Under magnification, the red platelets that are common in Oregon and Tanzania sunstone are apparent so the term sunstone is probably also appropriate in this case.