Chemical composition -- Typically a manmade mixture of silica, often containing some metallic oxide, although there are some natural glasses such as obsidian and tektite.
Color -- Virtually any desired color, often imitating some natural gemstone.
Optics -- R.I varies widely from 1.44 to 1.70 or higher. Singly refractive, but usually showing anomalous double refraction.
Durability -- Hardness usually 5-6.5. Brittle and heat sensitive.
Crystal structure -- Amorphous, often containing distinctive round gas bubbles and a swirled/whorled appearance.
Specific Gravity -- Varies widely from 2.0 to 5.0.
Glass has been used in many utilitarian and decorative forms for millenia and is often used as an inexpensive imitation of various gemstones, due to its easily altered appearance. It is sometimes referred to as "paste," especially when used to imitate diamonds or other transparent natural gemstones.
A manmade glass, usually colorless, containing finely dispersed metallic particles of copper or other metals, that superficially resembles sunstone.
A vivid green glass rpopularly mistaken to have been produced by the eruption of Mount St. Helens in Washington state (USA). According to the May 1999 issue of Jeweler's Circular-Keystone (page 36), this is actually a manmade glass that contains "rock dust" (not ash) from Mount St. Helens. It is distributed by Emerald Fox in Seattle and Leavenworth, Washington. It is also sometimes misleadingly called "emerald obsidianite." The material enjoyed some popularity for a few years following the explosive eruption in 1980 but now seems relegated to gift shops in the area. |