|
Labradorite
This is a sodium-rich plagioclase feldspar which
display~ particular type of iridescence on a dark ground.
The nar labradorite is derived from its main source: Labrador,
Canada. The effect is probably due to the presence of ve fine
platelets of different compositions and minute inc sions of
ilmenite, rutile and, perhaps, magnetite, whi cause diffraction.
Appearance The ground color is a dark smoke
gray, t when light strikes it in a particular direction, it
displa. striking rainbow-colored reflections (violet, blue,
gree yellow, and even orange and reddish) known as labradorscence.
It is cut into gems, or small, not too convex, Gished plaques
for setting. It is also used as an ornamenmaterial for carving
and engraving. The background cc is uninteresting and it is
the strength of the labrador scence that gives the stone its
value. The particula brightly colored variety found in Finland
is sometim known as spectrolite.
Distinctive features It is highly distinctive
at first sigbut there is an ornamental material, used in slabs
and cc sisting of a rock containing large pieces of potassic
fe spar, which looks similar to labradorite. This mater, which
is called larvikite after the place where it is tounc Norway,
is used for building purposes only.
If necessary, the two could be distinguished by their derties.
Occurrence The labradorite used in gems comes
maifrom Canada and Finland.
Value Quite low, partly because it is hard
to use. Ftypes of work can bring out its characteristic colors.
Simulants and synthetics It does not appear
to ha. been imitated or produced synthetically.
|
