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 (brown)
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
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
Old Rock Turquois
Old rock turquoise is an old Persian (Iranian) turquoise term for
very high quality turquoise (sky blue, veinless turquoise that retains
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 quartz).
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
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 Cat's-eye.
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 mosaic gold.
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).