Heliodor

From The Gemology Project
Revision as of 08:02, 21 June 2009 by Barbra (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search
Heliodor
Chemical composition Be3Al2(SiO3)6 Beryllium 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)
Faceted Heliodor
Photo courtesy of Rick Martin, Art Cut Gems
3 phase inclusion in heliodor
Photo courtesy of Connie Forsberg

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 the Ukraine in Russia, and also in Connecticut and Maine in USA.
Heliodor is considered a talisman for those named Hugh.