The opaque gems include representatives of metallic ores and rock-forming

minerals, and with the exception of jade they are used mainly as ornamental

stones. Some opaque gems such as obsidian, a volcanic glass, and jet, an

extremely hard form of coal, are better classified as rocks. (An unusual mineral

that rightfully belongs to this group is the pearl because, as with all gems, it

is highly prized for its beauty.)

Turquoise is a sky blue gemstone that has been used as an ornament since

the dawn of civilization. Jewelry made from turquoise has been found in

Egyptian and Sumerian tombs, dating back to the fourth millennium B.C.

Because of its softness (slightly less than 6 on the Mohs’ hardness scale),

turquoise was easily worked with the primitive tools available in ancient times.

The demand for the gem in the United States has been high because of the

popularity of turquoise jewelry made by Native Americans in the West. For

ages, the gem has been admired by the Navajos, who mined it long before the

arrival of the Europeans. Most deposits were in New Mexico, Arizona,

Colorado, and Nevada. The mineral is associated with copper and occurs in

nuggets or in veins. Sometimes tiny veins of clay and iron oxide crisscross the

stone, giving it a much greater appeal.

Jade has been highly regarded since ancient times for its pleasant green

color and versatility. It is a waxy or pearly mineral that is usually green but is

also yellow, white, or pink. Unlike other gems, which are usually varieties of a

single mineral, jade has complex mineralogical attributes. It occurs in two varieties

that are of different chemical composition but are similar in appearance.

Jadeite is a pyroxene, and the light, translucent emerald green form is considered

a precious stone. It is regarded as the more valuable of the two jades

because it has a richer appearance and possesses a greater variety of colors.

Nephrite is an amphibole and the more common of the two jades. Both varieties

of jade have been carved into ornaments and implements since antiquity.

Moonstone, which is a variety of plagioclase called albite, is valued as a gemstone

because of its bluish white or pearly opalescence. It receives its name from

a moonlike silvery white sheen that changes on the surface as the light changes.

Almost all moonstone of commercial value is from mines in Sri Lanka (Ceylon)

off the southern tip of India. One belief is that knowledge of the future can be

obtained by holding a moonstone in the mouth under a waning moon.

Malachite is a common ore of copper, and because of its conspicuous

bright green color, it is a useful guide in copper prospecting. It is often found

together with azurite, which forms deep blue crystals. Both occur in smooth

or irregular masses in the upper levels of mines. Malachite sometimes possesses

crystals with a glassy luster but usually occurs in fibrous rounded masses

with a silky luster. The compact, deep-colored stones make beautiful ornaments

when cut and polished. Malachite is also fashioned into urns, bowls, and

a great variety of art objects. In the Middle Ages, malachite was especially treasured

as a protection against the "evil eye."

Lapis lazuli (lazurite) has been in high favor as an ornamental stone for

thousands of years. Deposits in a very remote part of Afghanistan were mined

more than 6,000 years ago. It has an intense purplish blue color, which, unlike

that of many gems, does not fade in sunlight.The stone is used to make a variety

of art objects and can be cut into a gemstone, although its softness does

not make it entirely suitable for this purpose. An old tradition holds that the

Ten Commandants were inscribed on two slabs of this stone.

Serpentine is another ornamental stone, composed of a mixture of magnesium

and iron-aluminum silicates and water. It also might contain small

amounts of iron or nickel. Serpentine is translucent to opaque with a greasy

or waxy luster and varies in color from cream white through all shades of

green to black. Serpentine, so named because of its mottled green color, like

that of a serpent, is soft and easily polished and can be worked into a variety

of ornaments and decorative objects. An especially beautiful deep green form

used for indoor decoration is called verde antique marble.

Pearl, known as the queen of gems, has been treasured by civilizations in

all parts of the world for thousands of years. Even to this day, natural pearls are

among the most prized of gemstones. Pearls are formed by a number of marine

and freshwater mollusks such as clams and oysters when sand or some other particle

irritates the animal’s mantle that lines the inside of the shell. As a result,

layers of aragonite grow year by year into a spherical concretion with a

captivating iridescent luster. Pearls are also grown commercially by artificially

implanting seeds inside oysters.Pearls might also be gold, pink, red, or black.The

pearl was once esteemed as the emblem of purity, innocence, and peace.

Amber is a metamorphosed resin from ancient tree sap buried deeply

under high pressures for up to 100 million years or more.The most extensive

deposits occur along the Baltic Sea and represent extinct flora of Tertiary age.

Most amber occurs in shades from yellow to brown, but some specimens are

opaque white. Often insects and even small tree frogs become trapped and

preserved in amber. The process by which resin preserves tissue so that it

retains its original size is still a mystery. Air bubbles captured in amber from

the Cretaceous period indicate a much higher atmospheric oxygen content,

which might have contributed to the giantism of the dinosaurs. Even deoxyribonucleic

acid (DNA), which constitutes the molecules of heredity, has been

extracted from extinct species trapped in amber.Wonderfully preserved specimens

in amber make it a valuable gemlike stone.

Joseph Kieffer

http://hand-made-jewelry.com