Pyritic Inclusions in Oregon Sunstone
Figure 1. Reflected light reveals the metallic luster of these colorful inclusions in an Oregon sunstone. Photomicrograph by Rosie Young; field of view 1.26 mm. Courtesy of GIA Museum, collection no. 4735.
Figure 2. Left: The yellow color of the inclusions can be seen with brightfield illumination, with those having a copper core appearing dark in the center. Right: The same view with reflected light shows the metallic luster of both the pyritic inclusions and the copper. Photomicrographs by Rosie Young; field of view 1.26 mm.
A sample of Oregon sunstone from the GIA Museum’s collection was found to contain some unusual inclusions that appeared yellow in transmitted light and iridescent in reflected light. Vivid shades of yellow, blue, and purple were visible in a concentric pattern when illuminated with a fiber-optic light (figure 1). Some of the inclusions contained a metallic copper center and appeared darker than the surrounding inclusion under brightfield illumination (figure 2). The series of parallel lines pictured are also thought to be copper inclusions.
These inclusions looked pyritic in nature and possibly altered as a result of heating. This may well be natural heating from processes within the earth, as Oregon sunstone is not known to be treated.
