It consists of feldspar, mostly plagioclase and mainly oligoclase, some andesine and labradorite and has a characteristic appearance: there is a flicker of small metallic flakes inside an orange mass, this is why it was given the name of sunstone, or héliolite.
This orange optical effect is caused by thin layers of hematite or goethite on which the light is reflected flickering, sometimes in blue or green, this phenomenon is also called aventurescence.
Furthermore the plagioclase feldspars often show a Schiller effect or adularescence / labradorescence (due to the superposition of different plagioclase strips that interfere) which adds to the sparkle of glitter metallic inclusions.
The variety from Oregon in the United States (Oregon Sunstone), consisting of labradorite and discovered in the 1980s contains micro particles of copper instead of hematite that enhance the color orange. It can also be green, yellow, pink, brown, colorless and often transparent…
It is also possible that the sunstone is made up of other plagioclase feldspars or even some alkaline feldspar microcline or ortoclase.
This feldspar is not to be confused with the “aventurine” quartz which contains fine particles of fuschite when its green, or of mica and hematite when it is orange.