Opal
Consumer Information
What
color is it?: Opals
can be any color your can imagine. From the blue green opal you
see at the top of the page, to the orange color of the fire
opal that you see in the photo on the left.
What is the story behind this gemstone?: Opal averages between 10% to 15% water. But it is a rather unusual formation of sphere that line up in a geometrical pattern that gives opal its play of color. These tiny spheres serve to cause defraction of light like a prism, which causes the colors in opal.
Can I wear it everyday?: Well, yes and no. Because opals contain water they can be fairly brittle. And they need to be oiled to keep the water inside. But as long as you are not framing houses or digging ditches, you can wear opals like every other gemstone. Just keep in mind that they will chip easier than other gemstones.
Is it
expensive?: Opals range
from very inexpensive stones which are the almost pure white milk
opals, to the very expensive black opals. In
between you will find a huge range of colors and prices including
the boulder opal pictured below.
Is it a birthstone?: October. But let's get one thing straight. I have heard a lot of people say that they cannot wear opals because it is not their birthstone. And that its bad luck to wear an opal if it is not your birthstone. I guess if you believe that old wives tale enough it might come true. But I have never heard of anyone suddenly having a streak of bad luck simply because they started wearing an opal when it was not their birthstone. So don't let that worry you. It isn't true.
What
do I need to know before going shopping?: There are several opal imitations and even some
synthetic opals on the market. So you should be sure to shop with
a qualified gemologist/jeweler. Also, take time to inspect the
opal very carefully before you buy. Opals that have been left
in a hot showcase too long can get what is known as crazing.
This is the appearance of tiny cracks and fissures where the heat
has dried the water out of the stone and caused it to crack. Also
be aware that temperature changes can crack an opal. Taking your
hand out of your freezer and immediately reaching into a hot oven
for tonight's dinner rolls can cause an opal to crack due to sudden
and extreme temperature changes. So if you are cooking dinner,
or if you live in a city where it gets very cold you might want
to reconsider leaving the opal in your safe and not wearing it.
And of course, don't wear your opal while framing houses or pouring
concrete either.
..
General Information
Extremely rare 6 and 3 rayed Star Opal courtesy of Idaho Opal Mines, Inc. Thanks to Bob and Susan Thompson. Visit them by clicking HERE.
Source: Australia, Brazil, United States, and other locations world wide
Chemical: SiO2
Formation: Opals form when silicon in silicon-rich soil fills in voids left in the ground, most commonly by decaying trees. The Petrified Forest in the United States is actually an area where ancient huge trees fell and decayed. The silicon from the soil leached into the void and created an opalized tree in the original living tree's form. Most of the finest opal in the world comes from Australia, although Brazil has recently reported some excellent finds of opal.
Crystal System: Amorphous
Unusual Properties: Play of Color due to light interaction with water inside the opal.
Gemological Information
Opal in matrix rock
RI: 1.450
Birefringence: None
Optic Character: Single Refractive
Specific Gravity: 2.15
Hardness: 6 average
Transparency: Opaque to TP
Special Identifying Properties and Tests: Play of color, low refractive index, SG, magnification should be diagnostic.
Synthetics: Gilson synthetic is easily identified by its snake skin appearance. I have slides of this material that I will be adding. Glass imitations are easily identified by their coloration and varying RI.
Imitations: Many