Only a few of the materials we call gems are not of mineral origin. The so-called organic gems include pearls and mother-of-pearl, amber coral, ivory, jet, and shell.
Amber is the hardened, fossilized resin or sap of ancient pine trees. Various species of pine trees produce different types of sap, so there are several types of amber with varying compositions. The material is usually amorphous and occurs in lumps displaying a resinous luster.The hardness is 2-2 ½ on the Mohs scale, so amber can easily be cut with a pocket khife. The specific gravity is very low, about 1.2,and amber will float in sea water. This is a good test for genuine amber, since most imitations will sink in a saturated water solution of salt. The low S.G. also allows amber, released from sediments, to be washed up on shore by wave action. Such pieces may be sand size or reach a weigh of many pounds.
Amber can be dark brown to pale yellow, orange, red, whitish, greenish, bluish, or violetish. The most common colors are orange, yellow, and brown; the other colors are usually caused by light interference of bubbles of air inside the material. Natural amber is generally termed “block amber” and includes the following types; cloudy or bastard amber contains many small bubbles; fatty amber is translucent,also full of small bubbles and resembles fat;clear amber is transparent.
Some amber is mined, rather than recovered from seashores; this has been termed “pit amber” is opaque and soft, resembling bone or ivory. Exposure to sun and sea water may cause amber to turn opaque and chalky, with a “foamy” or frothy appearance.
Extensive deposits of amber are found on the shores of the Baltic Sea. Much amber is recovered at the shore, but considerable amounts are mined. The amber washed ashore is released at the sea bottom from the sediments in which it has been preserved. These sediments are millions of year old. Since amber sometimes contains the remains of insects that were trapped in the sticky tree sap of an ancient pine tree, we may thus learn something about ancient insect life by studying amber that formed at different times.
In addition to the Baltic amber, there is dark-red or orange Sicilian amber; Roumanian amber, Characterized by a brownish-yellow color and the presence of considerable sulfur; and Chinese amber, actually primarily from Burma, dark brown to brownish-yellow in color, sometimes colorless or red, and often heavily crazed.
Reconstructed amber or pressed amber (“amberoid”) is man-made, and produced by melting small bits of amber together under pressure. This material is also sometimes dyed various colors.
Amber is easily distinguished from plastic imitations by means of a needle, heated to redness. The hot needle is touched against the suspected amber, usually in an unobtrusive place, such as just inside the hole in a bead. The hot needle will burn the material, and the odor of the smoke is distinctive. Plastics give off a strong, rancid smell of camphor and carbolic acid, both of which are strong, penetrating, and unpleasant. Amber gives a pleasant, sweet smell. But other natural resins, such as copal, also give sweet odors when burned, and other tests are needed. A good test to distinguish between amber (and other natural resins) and imitations is cutting with a sharp knife. When cut, natural resins tend to chip and break into powder. Plastics and bakelite yield large chips or curled peelings.
Amber is in great demand, especially among collectors of antiques. Sicilian amber is highly prized, And transparent red or green material is the most valuable, followed by transparent yellows. Natural amber may darken with long exposure to the air, turning a mellow brown color. Pressed amber, on the other hand, may turn white as it ages. Amber is used extensively to make beads, boxes, and ornamental carved objects, and has maintained its popularity for more than 2,000 years.
Coral has been popular for thousands of years. Its curative powers were strongly believed by the ancient Romans. A piece of red coral was supposed to change color according to the state of the wearer’s health. Superstition about coral was prevalent, but its Magical powers would only be effective if the coral were not carved or fashioned by man. Coral held a treasured place among the inhabitants of Persia, Tibet, India, and Africa. Strings of coral were considered royal gifts in some parts of Africa, and coral was sacred in India two millennia ago.
Indians of the southwestern United States have known and prized coral for more than four centuries. Today some Indian tribes, especially the Zuni, still employ coral in their silverwork, although much of the red material used is red abalone.
Coral is the accumulated exudation of tiny marine animals. These animals, called “coral polyps,” live in huge colonies and exude a deposit of calcium carbonate, the mineral calcite, to form a protective home. A coral colony always grows perpendicular to the surface of attachment. The calcium carbonate accretion formed by the polyps is the material we know as coral.
There are many varieties and colors of coral. White coral is the most common; other colors include pink, orange-pink, orange, blue, red (“precious coral”),and black (“king’s coral”). Coral occurs throughout the world in warm climates and tropical waters having a temperature above 68 F. The most important sources are the Mediterranean Sea, especially along the coasts of Algeria, Morocco, Tunisia, Sardinia, and Italy. Coral usually grows in shallow water, but some varieties form at depths of 1,000 feet. The structure of coral is very distinctive: a branched, tree-like shape. Individual branches may show a fine scale striping or banding. The only common imitations are wood, wax, and celluloid, but these can usually be distinguished on the basis of hardness and microscopic examination.
Gem quality coral is uniform in color and dense enough to take a high polish. The value of any particular color is matter of local fashion, but the deep-red variety, sometimes called. “ox- blood coral,” Generally commands higher prices. Pink and pale-colored, sometimes called “angel’s-skin,” can be even more expensive, and a fine, well matched strand of beads may cost several thousand dollars. The finest coral gems come from ltaly, and include beads, cameos, intaglios, figurines, carvings, and handles.
Ivory is generally considered the material forming the tusk of an elephant, but may also include other animals, such as the hippopotamus, walrus, wart-hog, And the narwhal, an Arctic whale. Elephant ivory has a distinctive spiral structure not seen in other kinds of ivory.
Ivory is very dense material, and is essentially the same substance of which teeth are composed. Its pores are filled with an oily compound that adds to the luster of its polish, and makes ivory easy to carve. Elephant tusks are actually enlarged incisor teeth, and may reach a length of 10 feet and weigh nearly 200 pounds.
Carved ivory objects have been found in tombs several thousand years old. Thrones of ancient monarchs were adorned with ivory carving and ornaments. Fine and detailed ivory sculptures decorate museums and private collections throughout the world.
Most genuine ivory comes from Africa; exports are regulated, but a large quantity of ivory is illegally traded. Typical fabricated ivory objects include necklaces, cuff link, studs, rings, bracelets, clips, umbrella handles, piano keys, figurines, boxes, and billiard balls. Ivory is porous and easily stained. It has a tendency to turn yellow with age, a process that has been attributed to atmospheric action. Exposure to sunlight can bleach and lighten the color of ivory.
Ivory imitations include bone, horn, plastics, and Plaster of Paris in nearly all cases a simple microscopic examination will suffice to distinguish ivory from imitation materials.
Jet is 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, times, especially worn to signify mourning for a deceased loved one.
Jet forms by the compression of lignite,a brown coal derived from buried driftwood. The classic locality is Whitby, Yokshire, which is the locale of one of the world’s oldest gem industries, specializing in the production of jet. When recovered from its host rock, Whitby jet may sometimes have the form of the original wood branches and logs. Other localities for jet include Spain, Germany, France, Nova Scotia, Colorado, and Utah.
Jet has a dull luster on broken surfaces, and a hardness of 2 ½-4 on the Mohs scale. It is tough and Takes a good polish. Imitations include dyed chalcedony, black tourmaline, garnet, and obsidian(all are harder than jet and feel colder to the skin); bakelite (pungent odor when heated); glass (vitreous luster on broken surface); rubber, notably a hard variety called vulcanite, but this is easily distinguished Because give a 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.
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 of 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 a pink background, or vice versa.
Interesting objects, sometimes seen in jewelry, that resemble eyes are shell with circular markings. This material is called operculum.