Opal How to Guide
History and tidbits
The word Opal is from the Roman
word “opalus” which was derived from the Greek word “opallios” and both have
the meaning “change of color”. Opal has a long history of ancient times being
mentioned in the Bible were Opal in Hebrew means “precious stone” This was one
of the 12 stones to be placed on the high priest breastplate dating back to
about 1300 BCE.
A writer named Sir Walter Scott started a rumor that could have damaged the Opal market back in 1829. One of his novels created a superstition that Opal was a bad luck charm. He must have been a pretty good writer because this created a decline in the Opal market. However, someone stepped in to set maters straight because she loved Opal and knew this was poppycock, and the one that dispelled these rumors was none other that queen Elizabeth herself.
The Andamooka Opal Necklace
The cutting
and polishing were completed by John Altmaan, and the final stone weighs a
whopping 203 carats. It was set it into an ornate scrolled necklace made of
diamonds set in 18 carat palladium and included matching earrings and a
pendent. This fabulous Opal was presented to the Queen in Adelaide in March
1954 on behalf of the people of South Australia.
Opal is
one of the few gemstones that can claim to be considered a “precious gemstone”
in the company of diamonds, rubies, and emeralds’ and pearls. Opal is a
beautiful and the most colorful of the precious gemstones. opal is made
up of water and silica (the main component in glass). In late 2008, NASA announced it had discovered opal deposits on Mars.
Opal is a hydrated amorphous form of silica (SiO2·nH2O);
its water content may range from 3 to 21% by weight but is usually between 6
and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are
classed as minerals. It is deposited at a relatively low temperature and may
occur in the fissures of almost any kind of rock,
being most commonly found with rhyolite,
limonite, sandstone, marl,
and basalt. Opal is the
national gemstone of Australia.
Types;
We will look
at three types of opal, common, precious, and other. Precious
opal displays play-of-color (iridescence), common opal does not. Play-of-color is defined as
"a pseudochromatic optical effect resulting in flashes of colored light
from certain minerals, as they are turned in white light." The
internal structure of precious opal causes it to diffract light,
resulting in play-of-color. Depending on the conditions in which it formed,
opal may be transparent, translucent or opaque and the background color may be
white, black or nearly any color of the visual spectrum. Fire opals that
do not show play of color are sometimes referred to as jelly opals. Mexican
opals are at times cut in their rhyolitic host material if it is hard enough to
allow cutting and polishing. This type of Mexican opal is referred to as a
Cantera opal. Also, a type of opal from Mexico, referred to as Mexican water
opal, is a colorless opal which exhibits either a bluish or golden internal
sheen. Kinds
of common opal include the milk opal, milky bluish to greenish (which can sometimes
be of gemstone quality); resin opal, which is honey-yellow with a resinous
luster; wood opal, which is
caused by the replacement of the organic material in wood with opal. Common opal often displays a hazy-milky-turbid sheen
from within the stone. In gemology, this optical effect is strictly defined as opalescent which
is a form of adularescence (as
in a moon stone). As for precious opal
we will look at the localities next.
Precious Opals
Without a doubt Australia is the Opal
capital of the world, other significant deposits of precious opal around the
world can be found in the Czech Republic, Canada, Slovakia, Hungary, Turkey,
Indonesia, Brazil, Honduras, Guatemala and Nicaragua, and the USA.
The world's largest and
most valuable gem opal "Olympic Australis" was found in August 1956 at
the "Eight Mile" opal field in Coober Pedy. It weighs 17,000 carats
(3.4 kg; 7.5 lb) and is 11 inches (280 mm) long, with a height
of 4 3⁄4 in (120 mm) and a width
of 4 1⁄2 in (110 mm).
Very high-quality
precious opal started coming out of Ethiopia about 1994.
Many south western states in the USA have
found Opal, the best of are probably the Virgin Valley opal fields in
northern Nevada produce a wide variety of
precious black, crystal, white, fire, and lemon opal. The black fire opal is
the official gemstone of Nevada. Most of the precious opal is partial wood
replacement. Notably opalized teeth, bones, fish, and a snake head have been
found. The largest producing mines of Virgin Valley have been the famous
Rainbow Ridge, Royal Peacock, Bonanza, Opal Queen, and WRT
Stonetree/Black Beauty mines. The largest unpolished black opal in the
Smithsonian Institution, known as the "Roebling opal", came out of the tunneled portion of
the Rainbow Ridge Mine in 1917, and weighs 2,585 carats (517.0 g;
18.24 oz). The largest polished black opal in the Smithsonian Institution comes from the Royal Peacock opal mine in the Virgin
Valley, weighing 160 carats (32 g; 1.1 oz), known as the "Black
Peacock.
Basic steps as follows are
just basic. Personally I like working opal slowly with a Dremel and keeping the material
cool with water, it is an option but beware opal will crack very easy if it gets hot
or is dropped, really, really take your time with this material. Also look for
the seam of opal when its dry, it may be a very thin layer, and it will be easy
to grind off your fire and destroy your opal or diminish its beauty. Line up
the seam to gain most of the fire and to chose how you will grind the bottom
for dopping.
Basics; Flatten the back
side of your material, to accommodate a dop stick. Do not use a flame to dop,
use a low temp or dopping glue, (some have had success using nail glue, its
water soluble and heat will cause it to fall off) on a slowly pre-heated stone.
Most dop pots have a flat area to lay normal sized Cabochons for preheating. Use
a wet grinding fine grit to slowly shape the stone avoiding over cutting into
the fire. 400 to 1200 grit is a reasonable range depending on how close you are
to the seam. The closer to the seem the finer the grit. The final step is the
polish cerium on wet leather will work well, again avoid heating this stone!
Where to find OPAL
The Royal Peacock
Opal Mine, some outstanding opal and notable fines from this location, that is
a pay to dig operation. Located at Virgin Valley Road, Denio, Nevada 89407 http://royalpeacock.com
The Rainbow ridge opal mine is also has been the site of many fine opals.
They also have a pay to dig site, located in Virgin Valley, Nevada https://www.nevadaopal.com
The Bonanza claims “the brightest Opals in the world” also a pay to dig
site. https://www.bonanzaopals.com
Free opals, I am not aware of any spots were you can dig free fire
opals, however there are many areas were you may dig common and jelly opal, one
such spot is Kramer hills in southern California, were some have found a much
desired hard to find cherry opal, others find yellow orange and I have heard
green, most opals are off with and browns, but you may get lucky. Look to the
local gem and mineral clubs for field trips into the area if you want a better
chance at success. The Victor Valley Gem and mineral club is a great local
group in the area. https://www.vvgmc.org/
Dremel polishing with nail glue guide. https://www.facebook.com/notes/heidi-eriksen/step-by-step-how-to-cut-polish-opals-with-a-handdrill/10150118940733035/
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