Sunstone is a distinctive variety of the mineral feldspar that exhibits a kind of reddish-orange metallic glitter. This optical phenomenon is caused as light reflects off minute inclusions of hematite or goethite (ger~tite). Both are iron oxide minerals. Rust is an iron oxide that forms when iron (hematite and goethite) combine with oxygen and water. Very occasionally the inclusions in sunstone are copper.
Due to the positioning of the mineral inclusions within the stone, the glitter effect which is correctly known as aventurescence can only be seen from certain angles.
In the 1800's sunstone was expensive due to its rarity but it's now more affordable because of new finds in several countries around the world. Some of the finest gemstones can be found in Oregon in the United States. This material known for its large crystals tends to be included with copper as opposed to hematite.