About Oregon Sunstones

Sunstone, the state gem of Oregon, is a rare form of Orthoclase Feldspar known as Aventurine Feldspar. Sunstones earned the name through the iridescent glow they sometimes exhibit when exposed to sunlight. This phenomenon, called Aventurescence, is thought to be caused by tiny copper plates in thin layers in various locations in the stone. The sunstone’s inherent color is clear or champagne color. The more scarce stones are the reds, pinks, oranges, and green sunstones. Very rarely found are the blue green and violet stones. The causative factors for the different colors was heretofore thought to be the copper impurities. Now this is under debate and research is still ongoing with X-ray Spectroscopy and chemical analysis. Commonly, the colored sunstones exhibit schiller which adds beauty to the finished gem. Colored sunstones often are found to be dichroic which means they can be green from one view and a deep red or orange viewed from another angle. Strangely enough, all green sunstones exhibit dichroism and show red when the viewing angle is changed. But not all red sunstones show the green dichroism. The sunstone crystal exhibits perfect cleavage and minimal bifringence, are considered triclinic and exhibit twinning on occasion.

Uniqueness. Sunstones make beautiful faceted gems and no two stones are alike with the exception of the champagne colored stones. To match any two cut stones, the only chance is to cut them from the same piece of rough stone. Every stone is unique. The rough stones come in the various colors mentioned above but can be cut to emphasize either the red or the green in dichroic stones.

Locations. Sunstones of these deep colors are found only in South Eastern Oregon near a tiny town called Plush near the Hart Mountain Antelope Preserve. Another deposit was found some 75 miles northeast near Berns, Oregon. Not much is known about the history of Sunstones since their discovery circa 1956. Historically, there is evidence found in ancient archeological digs that Oregon Modoc Indians used them for decoration and trade with other tribes.

Geology. Millions of years ago the Hart Mountain area experienced extreme geological upheaval with many volcanic eruptions and resultant lava flows and ash deposits. Sunstone molten liquid deposits formed in pockets in these ancient lava flows. As the lava eventually cooled, this liquid formed crystals which were trapped inside the solid magma. With subsequent pyroclastic flows, it is thought that these crystals melted and formed other shapes such as flattened plates and ovals.   After the valley cooled, an ancient lake covered this basin for thousands of years and slowly eroded away the basalt to expose the stones. Today sunstones can still be found on the surface of the desert floor in public collection areas.