oligoclase
oligoclase crystals from Arendal in Sweden
Detailed sheet
oligoclase
From the family of plagioclase, its name comes from the Greek “oligo”, a little bit, and “klassos” break, because it is a feldspar whose cleavage is more difficult than for others. It is part of the albite-anorthite series. It was identified by Breithaupt in 1826.
The heliolite variety or “sunstone”, orange colored contains inclusions of small crystals of hematite and goethite, it has the speckle effect (Schiller effect) and its inclusions sparkle like sequins.
A blue variety “azure-feldspar” is associated to lapis lazuli near the Lake Baikal in Russia.
CHEMICAL CHARACTERISTICS
(Na,Ca)[(Si,Al)4O8]
calcium - sodium alumino silicate
PHYSICAL CHARACTERISTICS
Main color
colourless
Other colors
white, blue, brown, grey, yellow, orange, pink, green
Color of streak
white
Luster
pearly, vitreous
Hardness
6.0 to 6.5
Density
2.61 to 2.68
Cleavage
perfect
Fracture
uneven
cleavage can be difficult, there is small flat surfaces on the fracture
OPTICAL PROPERTIES
Transparency
translucent, transparent
Refractive index
1.542 - 1.549
Double refraction
0.007
very weak, biaxial (+)
visible double refraction
No
Dispersion
0.012
Pleochroism
absent
Number of colors
1
Fluorescence
variable
often yellow
Inclusions
hematite, goethite
CRYSTALS PROPERTIES
often twinned tabular
crystals system
triclinic
OTHER INFORMATIONS
APPROACHING GEMS
Exploited
sites
It is found in France, in Auvergne, in Ariège, near the Vesuvius in Italy, in Afghanistan, Canada (Quebec), Tanzania …
use in jewelry
It is faceted or cabochon cut, used in fancy jewelery.
Daily care
and precautions
easy cleaning with water and dish soap
imitations and
treatments
artificial glasses containing glitters of brass mimic the varieties of sun stones.
Other
Gems
Venez visitez
notre site web
voillot-joaillier.fr
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