Sunstone is metallic in appearance and comes in red, orange or
green. However, cleaner red sunstone is very rare and commands true gemstone
prices. There are two main varieties of Sunstone. The stones from the USA
are plagioclase Feldspar that are colored by Copper. The other is a composition
of oligioclase feldspar, which also contains hematite or goethite inclusions.
The presence of Copper, Hematite or Goethite creates a reflection of light,
hence the name sunstone.
Sunstone is formed in molten lava and is discharged onto the
surface with the help of a volcano. The lava weathers away or is broken and
fine crystals of sunstone are then released. The hardness of the stone is
6.5-7.2 on the Mohs scale and its density 2.62 - 2.65.
The term “sunstone” is mostly utilized for specimens of
transparent to translucent feldspar that create intense, tinny flashes
especially when the light intermingles with small plate-like mineral inclusions
inside the stone. This visual fact is referred as “Aventurescence”.
Most of the sunstone’s deposits have been established in Canada,
India, Russia, and South Norway. Sunstone has also been discovered in the USA.
Sunstone occurs in a range of colors that begins with colorless
and ranges through yellow, green, orange and red. The color is determined, in
part, by the abundance and size of the copper platelets within the stone. The
copper platelets impart a green, pink or reddish color to the stone. Some exceptional
stones are deep green or blue in color.
Color can vary within a single stone. Some stones exhibit a
color gradient. They might be pink on one side of the stone and the color
gradually strengthens to orange on the other side of the stone. Other stones
have sharp color changes. These stones might have patches of green in contact
with an area of strong red color.
Some exceptional stones are pleochroic - their color depends
upon the direction of observation. The value of this gem-quality sunstone is
determined by its color, transparency, and the quality of Aventurescence.
Colorless and yellow stones are usually the least expensive and values increase
through pink, orange and red.