TRUGEMS Table of Contents Page
GOLDEN
SUNSTONE
What
is golden sunstone?
Golden
Sunstone is labradorite - a member of
the plagioclase group, within a family of minerals known as feldspars. Feldspars
are present in many of the exposed rocks of our planet. They are perhaps the
most abundant minerals in the earth’s crust and tend to be pale colored and
opaque. Transparent feldspars are extremely rare and are typically colorless. It
is therefore very unusual to find labradorite in brightly colored transparent
crystals. Golden sunstone is unique on earth in terms of its amazing clarity,
uniform saturated color, large average size and the polish attainable on faceted
surfaces.
Where does
sunstone come from?
SSunstone
is a product of dark-colored volcanic rocks, such as basalt. While basalt covers
thousands of square miles of the earth’s surface, only in a few scattered
localities does the rock contain large, distinct crystals of labradorite. The
best known such locality is the area near the city of Plush in western Oregon,
where sunstone occurs in a wide range of colors including pale yellow, beige,
pink, green, orange and red. Sunstone is the official state gemstone and
accounts for the majority of the value of Oregon’s gemstone production. The
colors in Oregon sunstone are caused by the presence of copper, which often
appears as metallic inclusions that reflect light and create an effect called
“Schiller”. Oregon sunstone is typically “cloudy” and translucent,
rather than transparent, and the yellow shades are extremely pale. Small cut
gemstones generally look “washed out” and the yellow shades are actually
almost colorless. Oregon sunstones in yellow, pink and coppery colors generally
range in size from about one to five carats; green and orange stones tend to be
smaller and are rare above five carats. The largest Oregon sunstone recorded
(known as “the Promise”) weighs about 54 carats and displays the
“Schiller” effect so typical for this locality.
What makes golden sunstone unique and different?
Golden
sunstone comes from a deposit unlike any other in the world. The feldspar in
this unique basaltic lava flow displays none of the pink, orange and green
shades typical of Oregon material. Rather, the sunstone here is totally
uniform in hue – a rich, golden straw yellow that appears to deepen in
large faceted gemstones. The crystals do not contain copper and are almost
always completely transparent. The average
size of crystals from this locality would yield cut gems between 3 and 10
carats, with stones over 20 carats available on a regular basis. Transparent
faceted gemstones over 100 carats have already been cut, making golden
sunstone by far the largest known cuttable plagioclase feldspar in the world.
The
hardness of golden sunstone is slightly greater than that of other feldspars,
and the material can be polished with the very high degree of reflectivity
normally seen only in extremely hard gemstones such as diamond, chrysoberyl and
sapphire. This unique reflectivity, combined with the relatively low refraction
typical of feldspar, creates a new phenomenon not observed in other gemstones.
Named “pseudo-dispersion” by noted author and gemologist Dr. Joel
E. Arem, this phenomenon results from the “capture” and reflection, by a
gemstone’s facets, of colors in the surrounding environment. These colors are
transmitted to the observer’s eye and appear
to be generated by and within the
cut stone, thus resembling the phenomenon of “dispersion” seen in gems such
as diamond. In fact, many jewelers have remarked that golden sunstone looks like
yellow diamond!
Is golden sunstone expensive?
Despite its great rarity and beauty, golden sunstone is surprisingly affordable. Cut gems are available in all the shapes common to manufactured jewelry and in sizes ranging from under one carat to more than 10 carats. Prices for these stones are in the range of several tens of dollars per carat, rather than hundreds or thousands! Unique, larger stones are individually priced.
©
Joel E. Arem 2000, 2002