Sunstone is a feldspar gem that glitters with reflections from tiny metallic platelets inside it. The effect is called aventurescence. Most sunstone is a plagioclase feldspar, either oligoclase or labradorite. Oregon sunstone, colored and spangled by copper, is the best-known variety and became Oregon's state gem in 1987.
What sunstone is
Feldspars are the most common minerals in the Earth's crust. Plagioclase feldspars form a series from sodium-rich albite to calcium-rich anorthite. Oligoclase sits near the sodium end and labradorite near the middle. Most sunstone comes from these two, though a few orthoclase feldspars show similar sparkle.
Sunstone is a cousin of moonstone and labradorite. The three are named for their optical effects instead of their mineral species.
Aventurescence and schiller
Aventurescence is a glittering sparkle caused by light reflecting off flat inclusions aligned inside a stone. In sunstone, the platelets are usually hematite or goethite in Indian and Norwegian material, and native copper in Oregon material. When the platelets are aligned, they flash together as the stone moves and give a coppery or reddish sheen called schiller.
The same effect, from different inclusions, appears in aventurine quartz. The gemstone optics page compares aventurescence with adularescence and labradorescence. The density and size of the platelets control the look. Fine platelets give a soft sheen. Larger, sparser ones give individual sparkles.
Oregon sunstone
Oregon sunstone is labradorite found in basalt lava flows in southern Oregon, mainly in Lake and Harney counties. It forms as crystals inside the lava and weathers out into the soil. Some deposits sit on public land where visitors can collect, and others are private claims.
Copper is what sets Oregon sunstone apart. It colors the stone and, in larger amounts, forms flat copper platelets that create schiller. Colors include pale yellow, orange, red, green and blue, and some stones show two or more colors. Some show a color change between two directions, which a gemologist describes as strong pleochroism. Red and green stones and those with strong schiller are the most prized.
Oregon sunstone is often clear enough to facet. Many stones are cut to show their transparent color, with or without schiller. It became Oregon's official state gem in 1987.
Oregon is also one of the few places where the public can dig for a gem on government land. The Bureau of Land Management has long kept a sunstone public collection area north of Plush in Lake County, where visitors may hand-collect stones for personal use. Rules and road access can change, so collectors check with the agency before a trip.
Oregon sunstone has no known treatment in normal trade. That stability is part of why it became the benchmark for copper-bearing feldspar.
Indian, Norwegian and Tanzanian sunstone
Sunstone from India is usually oligoclase or orthoclase with hematite platelets. It is orange to red-brown and often translucent to opaque. It is common in beads and cabochons and is the most affordable sunstone. Norway is a classic source, with oligoclase sunstone from the Tvedestrand area that owes its sparkle to hematite. Tanzania, Madagascar, Russia and Canada also produce sunstone.
Some feldspar shows both adularescence and aventurescence. Dealers usually sell such stones under their source name or a descriptive trade name.
The andesine controversy
In the early 2000s, red and green andesine feldspar appeared on the market in large amounts. Sellers said it came from deposits in the Democratic Republic of the Congo, Tibet or Mongolia, and some marketed it as a natural sunstone. The color looked similar to Oregon sunstone.
Gemologists became suspicious when the supply grew quickly and the reported locations could not be confirmed. Laboratory research showed that much of this material had been colored by diffusing copper into pale feldspar at high temperature. Field trips to the reported Tibetan deposits around 2008 to 2010 produced conflicting reports, and the debate ran for years. Many labs now report evidence of copper diffusion where they find it.
For buyers, the lesson is simple. Red feldspar from unconfirmed sources may be treated. Copper-bearing Oregon sunstone has a well-documented origin. Gem labs can test for diffusion, and the gemstone treatments page explains diffusion in more detail.
Judging quality
Sunstone value depends on color, schiller and clarity. Strong reds and greens and stones with even, bright schiller command the best prices. Transparent stones with visible color zones, such as red centers and green rims, are also prized. Cutting matters. A cutter orients the stone so the schiller shows face-up, and with Oregon sunstone may balance color and sparkle.
Imitations include goldstone, a man-made glass with copper crystals. Goldstone shows uniform triangular or hexagonal copper flecks and is easy to separate under magnification. The page on glass in jewelry explains other glass imitations.
Durability and care
Sunstone has a hardness of 6 to 6.5 and perfect cleavage in two directions, so a hard knock can split it. Pendants and earrings face less risk than rings. For rings, choose a protective setting. Clean sunstone with warm soapy water and a soft brush. Avoid ultrasonic and steam cleaners and sudden temperature changes. The guide to cleaning jewelry safely has more detail.
Frequently asked questions
What causes the sparkle in sunstone?
Tiny flat inclusions of copper, hematite or goethite reflect light together. The effect is called aventurescence or schiller.
Is Oregon sunstone natural?
Yes. Oregon sunstone forms naturally in basalt and gets its color and sparkle from copper. It is not known to be treated.
Is sunstone a birthstone?
No. Sunstone is not on the standard modern birthstone list. The birthstones by month page shows which gems are.
How is sunstone different from goldstone?
Sunstone is a natural feldspar. Goldstone is man-made glass with copper crystals and has a more uniform glitter.