Plush
Plush
The Lake County, Oregon mining district producing copper-bearing labradorite known to the trade as Oregon sunstone
Plush is an unincorporated community and surrounding mining district in Lake County, Oregon, in the United States, and the locality name attached to a basalt-hosted feldspar deposit producing the gem material trade-named Oregon sunstone. The Plush sunstone is a copper-bearing labradorite — a calcium-sodium plagioclase feldspar — with metallic copper platelets dispersed through the crystal that produce aventurescence and, in the finest material, intense red, pink, and bicolour body colour.
Geology
The Plush deposit occurs in weathered basalt flows of the High Lava Plains, a Miocene to Pliocene volcanic province that covers much of central and eastern Oregon. The host basalts contain phenocrysts of plagioclase feldspar formed during slow cooling of the magma, with metallic copper introduced as an exsolution product during cooling. As surface basalt weathers, the resistant feldspar crystals are released into colluvium and surface gravels where they can be recovered by surface mining and screening.
The feldspar is labradorite by composition — typically An55 to An75 — and the copper occurs as discrete platelets aligned along crystallographic planes. Light reflecting from the platelets produces the aventurescence (also called schiller); copper in solid solution within the feldspar lattice produces the colour, with concentration determining the depth of red or pink saturation.
Production and market
Commercial mining at Plush has continued since the 1980s, with several active claim holders working the surface basalt and gravel deposits. Production includes colourless to yellow material, pink, peach, red, green, and bicolour stones, with the rare red and bicolour watermelon material commanding the highest prices. Most faceted Plush sunstone falls under five carats; larger stones in fine red colour are uncommon and trade well above the per-carat prices of the smaller sizes.
Oregon sunstone holds the designation of state gemstone of Oregon, recognised by the Oregon legislature in 1987. The Plush material competes in the international coloured-stone market with Tanzanian and Indian sunstone (typically of different optical character), and with the unrelated copper-coloured tourmalines and andesine feldspars from other sources.
Treatment status
Authentic Plush sunstone is generally untreated, and the colour and aventurescence are natural features of the material as mined. The Plush deposit is the recognised reference source for unenhanced copper-bearing feldspar, a status that matters in light of past trade controversies over diffusion-treated red feldspar from other origins marketed as natural sunstone. AGTA and GIA documentation of treatment status, and reliable provenance from a Plush-area producer, give buyers the necessary assurance.
In the trade
Buyers seeking Oregon sunstone should ask about specific mine attribution within the Plush district when available, and should expect untreated provenance as the default. The colour suite to evaluate ranges from pale champagne and yellow through green and pink into red and red-green bicolour, with bicolour stones showing clean colour separation across a single crystal commanding the strongest premiums. Aventurescence is a secondary character; the most desirable stones combine clean copper colour with subtle, even aventurescence rather than overwhelming sparkle.