Opals possess flashes of rainbow colors that change with the angle of observation, called play of color. This affect this effect is similar to the rainbow colors displayed on a soap bubble, only much more dramatic. This should not be confused with opalescence, which is the milky-blue or pearly appearance of opal caused by the scattering of light.
Black, Boulder, Ethiopian, Fire, Green, Jelly, Peruvian, Semi- Black, White
Opal |
October's Birthstone |
Major Sources |
Australia, Brazil, Ethiopia, Mexico, Peru, South Africa, Tanzania, USA & Zimbabwe |
Colors Found |
Various |
Family |
Opal: SiO2 + H2O |
Hardness |
5.5 – 6.5 |
Refractive Index |
1.37 – 1.52; SR |
Specific Gravity |
1.98 – 2.50 |
Crystal System |
Amorphous |
While tourmalines occur in large crystal sizes, gems of sufficent beauty to be set into jewelry are not available in great abundance. Because of their sizes, crystals are sometimes cut into long rectangular shapes following the axis of the crystal.
Green, Indicolite, Bi-Color, Paraiba, Rubellite
Tourmaline |
October's Birthstone |
Major Sources |
Afghanistan, Brazil, Kenya, Madagascar, Mozambique, Nigeria, Sri Lanka, Tanzania, USA & Zambia |
Colors Found |
Various |
Family |
Tourmaline: Complex borosilicate |
Hardness |
7 – 7.5 |
Refractive Index |
1.61 – 1.66; SR |
Specific Gravity |
2.82 – 3.32 |
Crystal System |
Trigonal |
©2011 America's Collectibles Network Inc. ♦ Gerald D. Sisk, JR. ♦ Guide to Gems & Jewelery ♦ Jewelry Television™