16.4.7: Heliodor

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Page ID: 4036

gemology
Gemology Project

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Heliodor
Chemical composition	Be₃Al₂(SiO₃)₆Beryllium aluminum silicate
Crystal system	Hexagonal
Habit	Prismatic
Cleavage	Poor, basal
Fracture	Conchoidal to uneven
Hardness	7.5
Optic nature	Uniaxial -
Refractive index	1.57 - 1.58
Birefringence	0.004 - 0.009
Dispersion	Low, 0.014
Specific gravity	2.7 - 2.9
Lustre	Vitreous
Pleochroism	Weak to moderate (shades of body color)

Heliodor is the golden yellow or golden green variety of the mineral beryl. It is a beryllium aluminum silicate. The golden color is produced when iron replaces some of the aluminum in the crystal structure. Heliodor can contain trace amounts of uranium, making it slightly radioactive. Heliodor was discovered in Namibia in 1910 in a pegmatite that also produced aquamarine, which is also colored by iron.
Crystals form very distinct hexagonal prisms that are some of the largest crystal examples in gemology. The largest faceted heliodor, 2,054 carats, is on display at the Smithsonian Institution in Washington D.C.
The name heliodor is Greek, meaning "gift from the sun". This stone is not often used in jewelry because it lacks brilliance and fire. Heliodor is found in Minas Gerais and Goias in Brazil, in Ukraine in Russia, and also in Connecticut and Maine in USA.
Heliodor is considered a talisman for those named Hugh.