History & Introduction
Onyx is an ancient gemstone, which was used for jewelry and as an ornamental gemstone
for carvings purposes. Onyx has traditionally been one of the most important engraving
and cameo gemstones with the most common form the black base with a white upper
layer. Though, onyx is a minor gemstone now, but the significance and value of the
stone has diminished as compared to ancient times.
Onyx is black and white banded agate (cryptocrystalline or chalcedony quartz). But
it is different from onyx marble, which is limestone. The banding of onyx is parallel
and consistent. Some varieties of onyx differ in color like sard onyx has a brown
base and white upper layer, cornelian onyx has a red base and white upper layer,
and Niccolo onyx consist of a thin upper layer, permitting the black base color
to show through as grey or blue.
Onyx name is derived from the Greek word "onux", which means fingernail; this could
be due to a Greek legend, in which Eros mischievously cut the fingernails of Aphrodite
with an arrowhead whilst she slept, and the gods turned the clippings into stone.
Onyx was cut and carved as a gemstone by the Ancient Greeks and Romans in cameos.
Intaglio etchings (negative relief engravings) were also created with onyx. These
carvings presented the banding of onyx.
Recognize - Onyx is easily recognized by its black base and white
upper layer with parallel banding, but, related to sard onyx the base is brown and
cornelian onyx consist of a red base. It is difficult to find out when the material
is a single color and is easily distinguished from agate when seen in the rough,
showing visibly parallel and banding consistently.
Availability - Onyx is available in countries all over the world,
including Argentina, Australia, Brazil, India, Botswana, Madagascar, Mexico, Myanmar
(Burma), Pakistan, Sri Lanka, Uruguay and the USA.
Usages - Onyx is usually cut into cabochons and beads and then
it is mainly used in earrings, bracelets, rings and necklaces. It is also an important
intaglio stone, and cameo and small statues and carvings are also cut from it.
Buying Guide
Color - Onyx has a black base and white upper layer, but may contain
bands of various other colors between these layers. In gemstones, onyx may come
in single color. In case of sard onyx, the color is brown to the base layer, cornelian
onyx has a red base layer and niccolo onyx consist of a thin upper layer, allowing
the black base layer to show through as grey or blue. Number of onyx gemstones are
totally black.
Clarity and Lustre - Onyx consists of waxed to dull luster and
is typically opaque.
Cut and Shape - Because it has its bands of color, onyx is often
carved into beautiful cameos which increases the banding. It is even cut into glossy
cabochons and even in faceted. Onyx gemstone is even drilled to make beads or pendants.
Treatment - Onyx is usually dyed to enhance its color and produce
a uniform hue. These processes were used many years. A black color is achieved with
the use of concentrated honey or sugar solution after heated sulphuric acid treatment.
Gemological Characteristics: