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OBSIDIAN
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) obsidian.
OCTAHEDRAL
A geometric object
with eight plane surfaces.
OILING
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 EUROPEAN CUT
A round Brilliant
cut with 58 facets, similar
to the old mine cut, first
appearing in around the 1880's.
It is characterized by a deep
pavilion, high crown, and
an open culet.
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 TURQUOISE
Old rock turquoise
is an old Persian (Iranian)
turquoise term for very high
quality turquoise (sky blue,
veinless turquoise that retains
it color).
OLIGOCLASE
(Also called Plagioclase)
A triclinic feldspar made
of soda-lime.
OLIVE
Olive is a term that
refers to a bead that is olive
shaped (elongated). This term
is mostly used in the USA.
OLIVELIA SHELLS
A kind of seashell
used for Heishi necklaces.
OLIVINE
(Also called "Chrysolite"
and "peridot") A
mineral composed of silica,
magnesia, and iron sometimes
used as a gem. Chrysolite
ranges in color from a light
pea green to a deep olive
green and an oily shine. It
is common in certain volcanic
rocks and meteorites. Mystics
have claimed that this lustrous
green stone drives away evil
and has special healing properties.
The name chrysolite has been
used in the past for yellow
varieties of tourmaline and
topaz.
OMEGA CHAIN
Unlike most chains
which are a series of linked
rings, an Omega chain is made
up of rectangular smooth rounded
metal plates set side by side
and crimped along the ends
onto a strip of metal mesh.
The end result is a fairly
stiff, yet flexible, circle
which needs to be worn high
around the neck since it is
not nearly as attractive when
viewed from the edges.
OMEGA BACK
These work a bit
like lever back earrings,
in that they have a hinged
lever on the back of the earring
near the bottom, but in this
case the lever ends in an
O shape that closes over a
post in place of a clutch
to secure the earring to a
pierced ear.
ONYX
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).
OPAL
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 firey 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.
OPAL BOUBLET
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
Opalescence is a
milky white/blue type of iridescence.
OPAL GLASS
Opal glass is a milky
white glass that mimics opals.
OPAL TRIPLET
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
Opaque means blocking
the passage of light (as opposed
to translucent or transparent).
OPEN-ENDED NECKLACE
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.
OPEN-WORK
A setting that has
open areas similar to filigree
cut which may allow for viewing
of the bottom of a stone.
See Basket.
OPERA-LENGTH
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.
OPERCULUM
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.
OPTICAL PROPERTIES
A gemstone's inherent
ability to interact with light.
Color, dispersion and fluorescense
are all optical properties.
ORA
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.
ORB
A part of coronation
regalia placed in the left
hand of the Sovereign during
the coronation as a symbol
of Kingly power. It is a globe
of gold encircled by a band
edged with pearls and set
with rubies, emeralds and
sapphires, joined by a perpendicular
band and surmounted by large
amethyst above which is a
jeweled cross.
ORE
A metal bearing mineral
from which metal can be profitably
mined or extracted.
ORIENTAL PEARL
A pearl that has
formed naturally with no human
intervention.
ORMOLU
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.
ORTHOCLASE
A variety of feldspar,
composed of potassium aluminum
silicate, characterized by
a monoclinic crystalline structure
and found in igneous or granitic
rock. Also called potash feldspar.
OURO VERDE
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).
OUVAROVITE
An emerald green
garnet composed of chromium
lime. Named from the Russian
Count Uvaroff. Uvarovite is
almost never used as a gemstone.
Distinguishing Uvarovite and
Tsavorite is difficult, but
an experienced gemologist
can do it.
OVAL CUT
A "fancy cut" diamond
or stone in an elliptical
shape like an oval.
OVERLAY
The upper layer of
an overlay technique. The
layer with the design.
OVERLAY TECHNIQUE
A decorative technique
involve two flat pieces of
silver, or other metal. The
top piece has a design cut
out of it and is highly polished.
The bottom layer is darkened
with oxidation to provide
good contrast to the design
on the top piece when the
two pieces are soldered together.
OXIDATION
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).
OXIDE
A compound containing
one oxygen atom per molecule.
See also dioxide.
OXIDIZE
The act of combining
with oxygen to make an oxide.Oxidized
metal is rusted.
OXYGEN
A nonmetallic element
that is normally a colorless,
odorless, tasteless gas that
constitutes 28 percent of
the Earth's atmosphere. Oxygen
combines with many other elements
easily. These compounds are
called oxides and make up
about half the solid matter
on Earth, making oxygen the
most abundant element present
in the Earth's crust.
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