Jet is a very hard variety of coalt

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Shell
The shells of many marine animals have an iridescent luster. Most notable among these are the shells of large pearl oysters and the abalone.

Shell is used for making mother-of-pearl buttons, handles, inlay work, and ornaments. Pauna shells from New Zealand and abalone from California waters are especially colorful. Sometimes a thin slice or abalone shell is cemented to the bottom of a colorless quartz cabochon to provide an interesting opal imitation.

Cameos are carved into the Helmet shell and the Queen conch, both of which grow in the waters of the West Indies.

Helmet-shell cameos are white and brown, while those from the Queen conch are white on .+ pink background, or vice versa.Interesting objects, sometimes seen in jewelry, that resemble eye, are shell with circular markings. This material is called operculum.

Shell

Jet

Jet is a very hard variety of coal. It may have been mined in England as early as 1500 B.C., and jet beads and charms have been found in ancient burial mounds. The material was popular in Victorian times, especially m to signify mourning for a deceased loved one.

let forms by the compression of lignite, a brown coal derived from buried driftwood. The classic locality is Whit by, Yorkshire, which is the ale of one of the world's oldest gem industries, specializing in the production of jet.

When recovered from its host rock, Whit by jet ma. sometimes have the form of the original wood branches and logs. Other localities for jet include Spain, Germany, France, Nova Scotia, Col¬orado, and Utah.

Jet has a dull luster on broken surfaces, and a hardness of 21/2-4 cu the Mohs scale. It is tough and takes a good polish. Imitations inclu6 dyed chalcedony, black tourmaline, garnet, and obsidian (all are hard,' than jet and feel colder to the skin); bakelite (pungent odor whe¬n heated); glass (vitreous luster on broken surface); rubber, notably a hard variety called vulcanite, but this is easily distinguished because it gives, burned-rubber odor when heated. Cannel coal is a substance much like jet that occurs in the coal beds of Newcastle, England, but this is more brittle than jet.

jet is customarily cut into beads, crosses, bracelets, cabochons, and various useful and decorative objects. The desirable attributes are pure black color with no inclusions and absence of fine cracks. Even the best jet is not expensive.