October Birthstone - Opal
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Opal fact file
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Crystal Structure: octahedrons
Chemical Composition: Quartz - Silicon dioxide, SiO2
Hardness: 5 ½ to 6 ½ MOHS
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Refractive Index: 1.43-1.46
Colors: Body color - white or tan or bluish.
Play colors - red, orange, yellow, blue, green etc
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Opal and Tourmaline are the
October birthstones. Opal is a gem of many colors.
This gem of sedimentary
silica has grids of silica spheres which show a play of colors created thru
diffraction. The size of the spheres determine the wavelengths and therefore the
colors seen. The brilliance of the colors are determined by the regularity of the
grid. These changing colors of opal has been used by literateurs down the ages,
from Shakespeare onwards, to symbolize a shifting mind and unsteadiness. There is
a superstition that suggests that it is bad luck to wear an opal if opal is not
your birthstone. Opals can deteriorate and change from a highly colorful, somewhat
glassy stone to a rather colorless mass of a chalky silicon dioxide. That is because
opals are unstable and are just one of the phases through which gel-like silica
(SiO2) can pass on its way to becoming stable crystalline quartz.
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September
