Obsidian (also called Apache tears) is a volcanic glass that is usually
black, but is occasionally red, brown, gray, green (rare), dark with "snowflakes,"
or even clear. This glassy, lustrous mineral is found in lava flows, and
obsidian stones can be massive. Obsidian is formed when viscous lava (from
volcanos) cools rapidly. Most obsidian is 70 percent silica. Obsidian has
a hardness of 5 and a specific gravity of 2.35. The pin above is Mahogany
Oiling is a process of applying mineral oil to a stone in order to enhance
it and mask inclusions, make them more transparent, and darken their color.
Emeralds are frequently oiled to mask their many inclusions.
Old Mine Cut
Old mine cut is a term that refers to a brilliant cut in which the stone
is cushion-shaped and has a high crown (the upper part of a gemstone).
Old Rock Turquois
Old rock turquoise is an old Persian (Iranian) turquoise term for very
high quality turquoise (sky blue, veinless turquoise that retains it color).
Olive is a term that refers to a bead that is olive shaped (elongated).
This term is mostly used in the USA.
Onyx is a semi-precious stone that is black and white, generally arranged
in layers. It is a form of agate with parallel banding. This structure
lends itself to cameo making. Onyx is a species of chalcedony (microcrystalline
Opals are semi-precious stones that are luminous and iridescent, frequently
with inclusions of many colors ("fire"). Opal is a mineral composed
of noncrystalline (amorphous) silica (and some water) and is a species
of quartz. There are three major types of opals: common opal, opalescent
precious opal (white or black, with a rainbow-like iridescence caused
by tiny crystals of cristobalite), and fire opal (a milky stone that is
fiery orange to red in color with no opalescence). Contra luz opals are
transparent opals that show a brilliant play of iridescence only when
light shines through the stone. Many opals have a high water content -
they can dry out and crack if they are not cared for well (opals should
be stored in damp cotton wool). Some opals are treated with oil, wax or
resin to enhance their finish. Opals have a hardness of 5.5 to 6.5 and
a specific gravity of 1.98-2.50. Opals are found in many places worldwide,
including Kenya, Czechoslovakia, Brazil, Peru, Honduras, Mexico, Canada,
and the USA -- but Australia has a tremendous variety of beautiful opals.
An opal doublet is a manufactured stone that is composed of two thin layers
that are glued together. A thin layer of opal is glued on top of another
mineral (usually a black onyx or ironstone, which enhances the stone's
color), producing a stone that is less expensive than a solid opal. Doublets
must be cleaned very carefully
Opalescence is a milky white/blue type of iridescence.
Opal glass is a milky white glass that mimics opals.
An opal triplet is a manufactured stone that is composed of three thin
layers that are glued together. A thin layer of opal is sandwiched between
a layer of clear quartz and a layer of either obsidian or ironstone. The
clear quartz is the top layer, making the gem harder (and less susceptible
to scratches). An opal triplet is an opal doublet with a quartz layer
on top. Triplets must be cleaned very carefully.
Opaque means blocking the passage of light (as opposed to translucent
An open-ended necklace has no clasp; it is worn by tying the ends together
around the neck. Open-ended necklaces usually have ornaments, like beads
or tassels, at the ends.
An opera-length necklace is a single strand that is from 30 to 35 inches
(60 to 90 cm) long. Opera-length generally refers to a string of pearls
that hangs to the breastbone.
The operculum is part of many shelled animals - it is the calcified, disc-shaped
"trap door" that opens and closes to protect the animal inside
its shell. The operculum from a species of sea snail called the Turban
Shell (Turbo petholatus, found in the South Seas north of Australia) is
eye-like with a natural cabochon shape and is used in jewelry. This jewelry
was popular in Victorian Era Britain. Operculum is also called Pacific
Ora was a costume jewelry company that was originally called Agnini &
Singer; it was founded by Oreste Agnini and Ralph Singer (born Raffaele
Cantaluppi) in Chicago, Illinois in 1921. They supplied the Eisenberg
company with its early buttons, brooches, and dress clips. The tradename
"Ora" was not adopted until the late 40s. Early pieces are unsigned.
Mr. Agnini retired in 1953 and Ralph Singer bought his half of the company.
The Company then became "The Ralph Singer Company" and continued
using the "Ora" trademark, which is a combination of the names
"Oreste" and "Ralph." When Ralph Singer died in 1963,
Raymond Pausback became a partner, running the company, and eventually
buying it. When he retired in 1984, he sold the company to Stanford Smith,
who ran the company until his death. His son, Stanford Smith Jr. then
ran the company. They still manufacture costume jewelry in Chicago, and
still uses the "Ora" trademark. They now sell jewelry online.
The Ora earring above is an old piece that is studded with clear rhinestones.
Ormolu (meaning "ground gold" in French) is an alloy of the
metals copper, tin and zinc that is used to imitate gold. Ormolu can also
be cast bronze or brass that is plated (gilded) with a gold and mercury
amalgam, giving it a gold-like look. Ormolu is used in frames, chandeliers,
candlesticks, and furniture ornamentation. It was very popular in Georgian
and early Victorian design. Ormulu can now also refer to any gold-like
metal used as decoration. Ormolu is also called bronze doré or
An extinct member of the cephalopod class with a long, straight, conical
shell which could grow as long as 60 feet. The interior is divided into
numerous chambers. These invertebrates swam the ocean by using a jet propulsion
type system that expelled water from the chambers thus pushing them forward.
They are related to the modern day squid, cuttlefish, and octopus and
date back 350 million years ago. Fossilized cephalopods are found in the
Sahara Desert, Morocco. Also, see ammonites.
Ouro verde (meaning "green gold" in Portuguese) is a type of
quartz crystal found in Brazil. This transparent stone is always irradiated
(to give it its pale, golden-green color).
Oxidation is a chemical process in which oxygen atoms bond to atoms of
a material (like a metal) and electrons are transferred from the oxided
material to the reduced material. Iron oxidizes when exposed to air and
moisture, forming iron oxide (rust). Silver oxidizes (tarnishes, turing
the surface black) when it is exposed to hydrogen sulfide in the air (forming
Ag2S, silver sulfide).