Gemstones & Pearls/Gemology
An example where the inclusion makes the gem
When you hold a shimmering sunstone from Oregon, its hard to resist its optical mirage. Tiny, sometimes eye-visible copper-platelet inclusions are responsible for this phenomena, called the schiller or aventurescent effect.
Schiller is generally directional, given the flat nature and alignment of the platelet inclusions. When light reflects off the platelets, you see the metallic sheen. Move the gem around and the schiller vanishes, leaving behind the gems subtler body color, ranging from colorless to yellow, orange, brown, green or red, depending on the copper content.
Sunstones belong to a group of gems called feldspars, which include albite, oligoclase, plagioclase and microcline families. The classic definition once dictated sunstones belonged to the oligoclase family and that the reflective platelets were hematite or goethite. But sunstone from Oregon is a form of labradorite, a variety of plagioclase feldspar; the inclusions are elemental copper.
Labradorite sunstone is produced mainly in the Rabbit Basin region of eastern Oregon. Production is sporadic, though Don Buford of Dust Devil Mining says he will increase output with an optical sorting machine that scans for color and pops the gems out of the ore with short, powerful blasts of air. Production is expected to increase 400%-500%.
This will dovetail nicely with increasing demand by designers and mass manufacturers, says Buford.
by Robert Weldon, G.G.
|Left: Peach-colored Oregon sunstone, just over 7.50 carats, has a gleaming schiller effect. Gem is courtesy of Dust Devil Mining, Cloverdale, OR; (503) 965-7707. Photo by Robert Weldon.
Right: Schiller can be observed in rough material. This makes it easier for cutters to orient the inclusions to show the best schiller effect through the table. Photo by Chris Carraher.