Sunstone

Sunstone is traditionally associated with the energy of the sun, confidence, leadership, vitality, optimism, drive, positivity and creativity. Because the flash thrown by the metal flakes within recalls sunlight, it is cherished today as a “stone that holds the power of the sun”.

Sunstone is not a designated birthstone in Japan, nor a designated anniversary stone. It was, however, named Oregon’s state gemstone in 1987, and is known internationally as a rare source-gemstone that symbolizes the state of Oregon.

Sunstone’s metallic flash is an optical effect called aventurescence (schiller). The platelet inclusions of metal or oxide minerals within (native copper, hematite, goethite and so on, by source) are aligned parallel to the feldspar’s (001) cleavage, and when light strikes, countless small plates reflect specularly in the same direction for a strong flash. Because the reflectors are well larger than the wavelength of light, it is on a different physical footing from moonstone’s Rayleigh-scattered “adularescence (blue-white glow)”.

Both are feldspar-group natural stones, but they differ in subseries and optics. Moonstone is an adularia/orthoclase (potassium feldspar, KAlSi₃O₈) and albite lamellar structure giving adularescence (a Rayleigh-scattered blue-white glow); sunstone is a plagioclase (Na-Ca feldspar) with metal/oxide plates giving aventurescence (a specular metallic flash). Their Japanese names, “moon feldspar” and “sun feldspar”, were coined for the symmetry of these two optical effects as the feldspar group’s “moon and sun”.

It is the world-famous sunstone mined in the Plush district of Harney County and eastern Lake County (the Ponderosa and Dust Devil mines) of Oregon, USA. A rare gem-quality sunstone of labradorite-to-bytownite plagioclase crystallized in basalt lava, it holds native copper (platelets of elemental Cu), is highly clear and can be faceted, and was named Oregon’s state gemstone on 4 August 1987. It shows a wide schiller of red, orange, green and blue, and is very highly regarded as a gemstone source.

It is a navigation tool from the medieval Scandinavian sagas (such as the *Saga of King Olaf*), the legendary mineral by which Vikings are said to have read the sun’s position on a cloudy day using its polarization. It is sometimes linked to Norwegian (Tvedestrand) sunstone, but modern scholarship holds the legendary mineral was more likely calcite (Iceland spar) or cordierite (iolite) (Ramskou 1967; reconstruction experiments by Ropars and others, 2011–2013). The prevailing view is that mineralogical sunstone (feldspar) and the legendary sunstone are probably different things.

At Mohs 6–6.5 sunstone is of standard feldspar hardness, but with perfect cleavage along (001) a hard blow can cause a directional break. It is safest to take it off where it might be knocked. Avoid ultrasonic and steam cleaners, as they can aggravate microcracks in feldspar. Wipe off sweat with a soft cloth, store it in its own case so it does not touch other stones, and avoid salt water and prolonged strong direct sun (a risk of color change).

As natural-stone jewelry, sunstone is used for raw-stone earrings, necklaces, rings, brooches and ear cuffs. TROZO makes sunstone jewelry that keeps the raw stone unpolished so its crystal faces and the flash of its metal inclusions (aventurescence) lead the design — both pieces you can choose by color and strength of flash from stock, and pieces where the meeting with the stone is left to chance.