Article - How To Buy opals On The Internet
“For in them you shall see the living fire of ruby, the glorious purple of the amethyst, the sea green of the emerald, all glittering together in a incredible mixture of light.”
- Written by Roman Pliny in the 1st century AD
This article aims to inform our buyers on best practices when buying opals.
Base Body Tone Guide
The base body tone guide is the best kept secret for buying opals on the internet, as most internet sellers give a fairly accurate description of the stones body tone that they are selling.
The opal association is marketing a body tone guide with opal stones and doublets so all buyers and sellers can have a uniform guide to gauge opal. These will help buyers compare opals between sellers. You should always buy off a seller who guarantees his product and grading so if you disagree you can return it.
The base body tone refers to the darkness or lightness of the opal ignoring the play of colour and brightness of the stone. The base colour can only be determined by looking down on the top of the stone and ignoring the material on the back of the stone. Only those stones ranking N1 to N4 are considered black opals. The opal price is determined by body tone, brightness, colour, play of colour, size and allowing for faults and imperfections.
See an example of an opal buying guide below:
Generally we have buying guides for sale on Opal Auctions in our Opal Literature category.
Brightness
The brightness of a stone is one of the most important factors in a stones beauty and value.
On the Australian opal fields you don’t hear the words” fire” used when miners talk about how bright a stone is. The term is however used a lot on the internet to describe a stone’s brightness, and to gauge opal brightness evenly over different stones.
Brightness Scale:
1 Faint, 2 Dull, 3 Bright, 4 Very Bright, 5 Brilliant - Gem Quality
This is the brightness chart you will see on most internet auctions with 5 being the brightest.
Currently the Opal association is working on a chart which will have seven levels of brightness with number ONE being the BRIGHTEST.
Check on listings to make sure what chart is being used.
Opal Colors are affected by Light!
Adjust Your Monitor for Accurate Colors + Contrast!
Your Opal will look different in different kinds of lighting. What color are seen, in what shape or pattern and from which viewing angles depends, in part, upon the viewing light used.
Sunlight and tungsten bulbs and warm bulbs lighting will tend to bring out more warm tone colours - reds, oranges, yellows magentas and purples. 'Cooler Light', like viewing your Opal in the shade, will tend to bring out the cooler greens and blues.
Light source. For viewing we suggest 12" to 16" from a bright tungsten light bulb. The best method is to have your back to a window on a sunny day with the sunlight coming over your shoulder.
Opal Sizes
Opal sizes are listed in millimetres (25.4 mm = 1 inch) and weights are listed in carats - just like all other gemstones and the jewelry mountings for them A calibrated shape gemstone should fit most jewelry mountings designed for those dimensions.
An opal that is within 0.5 to 1 mm of a calibrated size may acceptably fit into many calibrated mountings. Calibrated shape opals typically cost 15% to 50% more than a freeform shape opal due to the wastage of the opal when cut.
A freeform or larger size opal can be cut to a smaller size by an experienced cutter. Or you can have a custom jewelry mounting made for your unique opal, often for less expense than you might expect.
Thickness of the opal is a major factor in the carat weight of a precious opal gemstone - but an opal that is unusually thick will be considered less valuable as it may have to have excess weight removed to fit in a jewellery piece.
Play of Color
The very best precious opals have play-of-color across the entire gemstone when rotated. Most precious opals do not have play-of-color across 100% of the gem and are still stunning. Every natural precious opal gemstone is unique. Some precious opals have a flash, a Harlequin or other unusual pattern, rainbows, ribbons of color or many variations that are both beautiful and stunning while not covering 100% of the opal's face.
If an opal doesn't have Play-Of-Color, it isn't precious opal.
Sometimes an area of the opal will have a Play-Of-Color flash from a particular viewing angle, while another area of the opal flashes best at a different viewing angle. You may have to rotate or pivot the Gem Stone and/or change positions between you, the opal and the viewing light to see Play-Of-Color from a particular area of many opal Gem Stones. These stone are directional and are usually best suited to a pendant.
The most expensive opals have at least some wonderful Play-of-Color from most viewing angles. Sometimes an opal is at its best if lighted from the side or from slightly 'above' which would make it an ideal opal to use for a pendant. Some opals are at their best and brightest 'face up' - when the viewer has the light source over her shoulder to view the opal face-on like a ring stone. Some of these patterns can EXPLODE and look stunning.
Visible Opal Flaws
Listed here are some of the natural imperfections that can reduce the value of your precious opal. If you can accept these natural imperfections, you may be able to purchase an opal you otherwise couldn't afford. And, the 'natural imperfections' are proof that the opal is not man made!
A whitish to cream color area visible within your opal's surface is often called 'clay' or 'silk' or 'sand', small bits of clay present when the opal was forming. A 'Matrix' opal that has precious opal surrounded by visible rock or clay it formed within will be less valuable than a solid opal or most quality constructed doublets.
Potch lines across the colour face are acceptable provided they aren’t contrasting with the stones appearance .Most black gems have some potch in the face which doesn’t stand out but grey potch on a black stone would so it would decrease its value.
Sometimes a line inside the opal is just how the opal naturally formed and not a crack or flaw. Hold it close to a lamp shape to see it you can see a fractured reflection. If large areas of your opal have no precious Play-Of-Color (sometimes called 'potch'), that will reduce the value of the opal.
If there are visible scratches on the surface of the opal, its value will increase after the opal has been professionally polished to remove them. Cracks that go through the thickness of the opal's surface will reduce its value. To save a damaged valuable precious opal keepsake, cracks can sometimes be repaired and no longer be visible to the unaided eye.
Any seller of precious opals should always tell the customer if an opal has been repaired, stabilized or otherwise treated.
Opal Photography
It must be remembered that opal reflects light and digital cameras are not built to capture the amazing patterns and colour changes in opal.
A simple experiment is to place a stone on the floor by a doorway in natural sunlight, and move the stone back inside taking several photos along the way. You will most likely find that one photo looks amazing as if it has been enhanced.
Depending on the quality of photographic equipment and lighting sources, there will always be some variation between a digital photo and viewing a stone with a naked eye.
Sellers on Opal Auctions are expected to produce consistent photos that are representative of the opal being sold. Viewing an item that has a video can be a good way to reveal the many different faces of a good quality opal, and see the movement of colour that is not necessarily visible from all angles.
The experienced buyer will know to take all information into account, including the N tone rating, brightness, shape, dimensions and of course price.
The most common complaint is for blue opals. Most cameras capture the mauve in the stone which the naked eye can’t see. So if you see a mauve stone remember it’s most likely a blue stone.
Pastel colours seem to come out true to form. With Ethiopian opal the red is easy to capture and it will not be as bright in the hand.
If a seller guarantees his stock there is no advantage in over enhancing the pictures as he would have to return too much stock.
Many sellers use a black background as the camera captures the opal at its best. Always ask for a photo taken in the hand.
You can see the two stones below look better in the hand shot which is more natural. The last picture has been enhanced so you notice how the hand looks red and less natural. If you see a hand looking red you know the picture has been enhanced.
Viewing an Opal
With the opal in your hands, viewing in direct sunlight or 12”-16” from a bright tungsten or halogen light source:
- rock the Opal side-to-side and top-to-bottom
- pivot the Opal gemstone
- rotate it 90 degrees clockwise and repeat,
- then again.
Change the angle between the light source, the opal and your eyes and repeat. Rock the opal side to side or top to bottom to change the viewing angle.
Harlequin Patterns
Harlequin opal is the most sought after pattern in opal due to its rarity and beauty.
On the Gemological Institute of America (GIA) website, it states: “Harlequin or mosaic - broad, angular, close-set patches of color”.
Originally rounded or floral shapes were not called harlequin but this is now common practice.
On some unscrupulous internet sites many stones are listed as harlequin as the seller believes this will increase its value. Many of these stones would not be called harlequin on the opal fields, however they can still be beautiful and valuable in their own right. It is always important to buy from an opal expert.
In my 20 years experience of selling thousands of stones, I have only had three opals which I consider to contain a true harlequin pattern.
Doublet or Natural Stone?
It is difficult to determine if an opal is a doublet when it is set in jewellery. Only by removing the stone from the jewellery can you be certain.
Take a 10 powered loop or magnifying glass to the side of the stone. As glue doesn't polish you will see a gap between the crystal and backing so you know it’s a doublet.
Alternatively, if you have a digital camera you can take a photo of the side of the stone and enlarge the photo on your computer. If there has been glue used it will be easy to see.
See our article on doublets and triplets to learn more.
Inclusion or Fracture?
Some times stones have natural inclusions that look like fractures. The best way to determine if a stone is fractured is to hold the stone up to a base of a lamp shade and roll the stone in your fingers keeping the stone in the light and not the shaded area. If there is a fracture you will see the light reflect off the fracture like a chip in your windscreen.
Natural or Synthetic Stone?
Some synthetic or imitation opal can confuse customers.
Things to watch for:
- Usually they have no inclusions or potch backing behind them
- The pattern appears to be even through the stone which is rare except for top gems.
- If viewed from the side the line of colour is in the lower areas.
- Unnatural look and fire to them.
Synthetic opal are sometimes used in triplets which are much harder to spot. Generally they are very bright with a regular pattern that looks too constant to be natural. It is best to become familiar with a few man made opals (usually advertised as synthetic or man made) so it is easier to recognize them.
Andamooka Matrix
Andamooka Matrix is a natural white opal matrix found in Andamooka, South Australia. It has been treated to look like expensive black opal. The treatment is permanent but if you reshape or cut it you will have to re-treat it.
Some of this material is called concret which is more porous than the gem matrix. It is hard to get a good polish on it as it has pores. You can use a resin like liquid glass - or in Australia we use HX3 made by Shell. This is an epoxy that soaks in to the stone and gives a good polish. The colours and fire are amazing.
On the field they call this concret which is a horrible name for such a beautiful stone. Gem matrix, which you can get a natural polish on sells for $10 - 50 per carat while concret sells for $1- 2 per carat for larger stones.
Andamooka Matrix is even great just left in a glass jar as a dazzling specimen.
$1 No Reserve Sales
$1 No Reserve auctions are a great entry point for new opal buyers, as the buyer can determine the price at which the item sells. This is generally a good indicator of the value of the item.
Of course, the cost to the seller to list a $1 No Reserve item is going to be more than one dollar, once fees, buyer communication and shipping costs have been added to the price they paid for the item.
For this reason sellers have been known to list a great variety of high quality items to ensure a good selling price, and build up their loyal repeat customer base.
Rough Opal
Buying rough opal is always a bit of a gamble as you can’t really see the quality of the precious opal within.
You can lessen the risk if you buy “rubs”. Opal rubs are pieces of rough that have been rubbed down to the colour bar so you can get some idea of the stone it will cut. There is still the risk of inclusions in the stone which may make it smaller than you expect.
Most sellers on the internet wet the rubs or rough before hand to show the colours you can expect when it is polished. Always check the thickness of rubs as if it is too thin it won’t be strong enough for a ring. Any stone around 2 mm thick is too thin and may even need reinforcing in a pendant.
You shouldn’t expect to see a good stone in cheap rough as no seller would deliberately leave it there, however some beautiful stones have been found in rough that looked as if it contained nothing.
Black nobbys from Lightning Ridge are known for there surprises as even the most experienced dealers let some stones slip through in there rough grading process. Nobby rough untouched should always be viewed as a gamble.
With white opal rough it is a rule of thumb that what you paid per gram should cut that per carat as a finished stone.
Buying rough from photos is always difficult so you should check the sellers return policy. If they don’t offer one you should consider taking your business elsewhere. It is generally accepted that if you rub, snip or touch the rough it is considered sold.
Most internet sellers want your repeat business so even if you are not happy with what you have cut you can always ask for a bonus.
Trivia & Tips
- All items should be compared in the same lighting with no natural lighting to make comparisons. 100 watt globe 20 inches above stone recommended.
- Have a set of stones to compare what you are grading. Many buyers bring their own stones for comparison to the opal fields.
- If you are buying at Lightning Ridge in the motel there is strong sunlight in the morning so many sellers try to use this to their advantage.
- Buy from reputable verified sellers, not hobbyiests advertising themselves as experts - common place practice on other auction sites.
- On the opal field a clean stone with a N1 background and a brightness of 5 will sell very quickly for top money.
- Check a sellers return policy and stock guarantee. When returning stock use registered post.
- It might pay to test the waters with a seller on cheaper items if you are interested in purchasing an expensive stone.
The buyers on the internet have a big influence over the shape of the industry. If they return over enhanced stones back to sellers, they will be forcing sellers to more accurately classify their stock so all sellers are on an equal playing field, and it will be easier to compare stock between sellers.
The future is exciting for the opal industry. This beautiful stone is now available at competitive prices to buyers who would normally not have access to it.
The gemstone industry has many levels of dealers but the internet allows you to go direct to the source. New cameras will more accurately capture the true colours of opal and there will be evolving video technology that will allow you to see a stone as if it was in your hand.
With some knowledge there are bargains to be had today. Good luck with your bidding.
Contributors
- Paul Sedawie
President, Australian Opal Association
Every KnownVariety of Opal
Agate Opal. Banded variety of Opal.
Amatite. Opal in the form of thick mounds, formed from hot silica-rich springs. See also Geyserite.
Amber Opal. Opal with a brownish to yellowish background colour, resembling Amber.
Andamooka Opal. Opal from Andamooka, South Australia.
Banded Opal. Form of common opal with colour bands. Synonym of Agate Opal.
Bandfire Opal. Precious Opal with play of colours in wavy bands.
Black Opal. Precious Opal with a black, dark blue, dark green, dark grey or similar darkly coloured background or base
colour. Black Opal is the most valuable form of Opal.
Bone Opal. Opal pseudomorph after a bone.
Boulder Opal. Precious Opal from Queensland, Australia, found in the cracks of, or as coatings on, ironstone or sandstone boulders.
Cachalong Opal. Opaque, highly porous type of Common Opal.
Cherry Opal. Orange-red to bright red variety of Mexican Fire Opal.
Chloropal. Common Opal similar to Prase Opal, but with a lighter green hue.
Chrysopal. Common Opal similar to Prase Opal, but with a golden-green colour.
Claro Opal. Transparent Precious Opal from Mexico with an intense red, green, blue, and yellow play of colour.
Common Opal. Any Opal lacking play of colour.
Contra Luz Opal. Precious Opal where the play of colour is visible only when a light source is behind the stone. Coober Pedy Opal. High quality Precious Opal from Coober Pedy, South Australia.
Crystal Opal. Transparent to translucent Precious Opal where play of colour is visible on the surface and in the interior of the stone.
Dark Opal. Synonym of Black Opal.
Diatomite. Opal replacement of microscopic shells of diatoms (type of microscopic organism) clustered together. It is white, opaque, and chalky in texture. Synonym of Tripolite, Fuller's Earth, and Diatomaceous Opal.
Ethiopian opal form welo and Gondar ,new ly discovered opal fields dierect from opal wholesalers and miners
Fire Opal. Fire Opal is incorrectly used to describe Precious Opal, or Opal with play of colour. The true definition of Fire Opal is Opal with an orange to red colour. If the Fire Opal displays play of colour, it is more correctly known as Precious Fire Opal.
Flame Opal. Precious Opal where the play of colour consists of red streaks or bands that flicker like a flame when the stone is rotated.
Flash Opal. Precious Opal with large schillers that abruptly appear and disappear as the stone is rotated.
Flashfire Opal. Synonym of Flash Opal (above)
Fossil Opal. Opal pseudomorph of organic matter such as shell, bone, and trees.
Gelite. Opal (or Chalcedony) as an accessory mineral that acts as the bonding agent of Sandstone or other cemented rock fragments.
Geyserite. Opal formed from deposition of hot water springs. Also called Perlite, Fiorite, or Geyser Opal. See also Amatite.
Gilson Opal. Synthetically produced Opal.
Girasol. Yellow or orange variety of Precious Opal in which the play of colour seems to follow the sun as the stone is rotated.
Glass Opal. Synonym of Hyalite
Gold Opal. Common Opal with a golden hue.
Harlequin Opal. Precious Opal in which the play of colour is arranged in a consistent harlequin, diamond-shaped, or
rectangular-shaped pattern that is very vivid. Harlequin Opal is one of the rarest and most prized forms of Opal.
Honey Opal. Transparent to translucent Opal with an orange to orange-brown, honey-coloured background. It may or may not display play of colour.
Hungarian Opal. Any Precious Opal from Europe. However, nowadays this term often refers to any White Opal, regardless of where it was found.
Hyacinth Opal. Synonym of Girasol
Hyalite. Colourless, misty-blue, or sky-blue transparent variety of Common Opal. Usually forms botryoidal masses as well as strange and unusual forms. All Hyalite fluoresces green.
Hydrophane. White, opaque, highly porous Opal, that, when placed in water, allows the water to seep into it. This causes the stone to become transparent and almost invisible while in the water.
Iridot. Old name given to Opal for a short period of time when Opal had a reputation of causing bad luck.
Isopyre. Impure, dark red form of Opal. Isopyre was once thought to be a separate mineral.
Jasper Opal. Brecciated Jasper in which the cementing material is Opal.
Jelly Opal. A transparent Precious Opal with a gelatinous appearance and a bluish sheen. Jelly Opal may also refer to a
colourless, transparent Common Opal.
Lechosos Opal. Precious Opal with a milky-white background colour displaying a strong play of colour. May also refer to Opal with a strong green schiller.
Lemon Opal. Common Opal with a lemon-yellow colour.
Levin Opal. Precious Opal with long and thin, lightning-like flashes.
Light Opal. Synonym of White Opal.
Lightning Ridge Opal. Opal from Lightning Ridge, New South Wales Australia. Although different forms of Opal are found there, this term usually represents the high quality Black Opal found there.
Lithoxyl Opal. Wood Opal where the original structure of the tree is very apparent.
Liver Opal. Synonym of Menilite (below)
Menilite. Opaque, greyish-brown form of Common Opal. Also known as Liver Opal.
Mexican Fire Opal. Form of transparent Opal from Mexico, usually with an orange or red colour, highly desired as a gem. Although scientifically considered a Common Opal, it is rather rare and much sought after. If it exhibits a play of colour, it is known as Precious Fire Opal.
Milk Opal. Opal with a milky-white colour. Controversy exists whether the name Milky Opal is coined for a milky white Common Opal or a milky white Precious Opal.
Moss Opal. Common Opal containing inclusions resembling moss.
Mother of Opal. Precious Opal with bright colour specks filling the pores of sandstone or ironstone.
Mother of Pearl Opal. Banded Opal used as cameos.
Mountain Opal. Opal from igneous environments. Also called Volcanic Opal.
Neslite. Common Opal similar to Menilite, but darker grey in colour. It was once a popular material for sword handles.
Nevada Opal. Opal from the Virgin Valley (Humboldt Co.), Nevada.
Onyx Opal. Common Opal resembling banded Onyx.
Opal Matrix. Thin layer of Precious Opal on host rock. Small rock fragments are used in jewellery.
Opaline. Opaline is synonymous with Opal Matrix (above), but was also an old term used to describe Opal from Australia.
Opalite. Opalite has many connotations. It may refer to an impure form of Opal
Myrickite black glass. A yellow-green Common Opal with black inclusions an imitation Opal produced from resin
Opalized Bone. Synonym of Bone Opal
Opalized Fossil. Synonym of Fossil Opal
Opalized Shell. Synonym of Shell Opal
Opalized Wood. Synonym of Wood Opal
Painted Boulder. Sandstone boulders with a coating of Precious Opal. When used in jewellery, this term is synonymous with Opal Matrix.
Pearl Opal. Synonym of Tabasheer
Pineapple Opal. Opal pseudomorph after Ikaite that resembles a pineapple. It is found only in White Cliffs (New South Wales), Australia. The pseudomorphed mineral was originally thought to be Glauberite, but studies now prove it to be Ikaite.
Pinfire Opal. Precious Opal with very small, pinhead-size colour flashes.
Pinpoint Opal. Australian synonym of Pinfire Opal
Pipe Opal. Opal formed as a filling of long, cylindrical cavities in rock. Pipe Opals range in size from several inches to many feet.
Pitch Opal. Yellow to brown Common Opal with a pitchy lustre.
Potch. Australian term for Common Opal.
Prase Opal. Green to dark green form of Common Opal.
Precious Fire Opal. Fire Opal displaying play of colour.
Precious Opal. Any Opal exhibiting a play of colour.
Prime d'Opal. Synonym of Mother of Opal
Pyrophane. Precious Opal in which the play of colour wanders about and reappears at random. This term is sometimes
incorrectly used to describe Girasol.
Queensland Opal. Synonym of Boulder Opal
Quinzite Opal. Rose to pink coloured Opal. It is usually without play of colour, but a few examples displaying play of colour are known. Quinzite Opal is synonymous with Quinzite, Quincite, Quincite Opal, and Rose Opal.
Radiolite Opal. Common Opal of a smoky-brown colour caused by inclusions of the exoskeletons of a unicellular marine
organism known as radiolaria. May also be called Radio Opal.
Rainbow Opal. Precious Opal where the play of colour is seen in curved bands, somewhat resembling a rainbow.
Red Flash Opal. Precious Opal with red colour flashes that swiftly appear and disappear as the stone is rotated.
Resin Opal. Common Opal with a yellow-brown colour and resinous lustre.
Rumanite. Opal from Romania.
Seam Opal. Opal found in the seams or large cracks of rock. May also specifically refer to masses of white Common Opal containing bands of precious White Opal.
Semiopal. Term sometimes used to describe any type of Common Opal, but many times alludes to particular forms of
Common Opal, such as Wax Opal, Prase Opal, etc. Semiopal is also written as Semi-opal, and is synonymous with Half-opal.
Shell Opal. Opal pseudomorph after a shell.
Slocum Stone. A synthetically grown Opal. Also called Slocum Opal.
Sun Opal. Name that describes several types of Opal. May refer to Fire Opal, Mexican Fire Opal, Honey Opal, or Amber Opal.
Tabasheer. Opal occurring as an organic by product. It forms by the hardening of a secretion issued from certain bamboo, forming a porous, rounded mass of Opal.
Virgin Valley Opal. Opal from the Virgin Valley (Humboldt Co.), Nevada.
Wash Opal. Waterworn Opal pebbles from alluvial deposits.
Water Opal. Synonym of Jelly Opal
Wax Opal. Yellow to brown Common Opal with a waxy lustre.
White Cliffs Opal. Opal from the White Cliffs, New South Wales, Australia
White Opal. Precious Opal with light body colours (white, yellow, cream, etc.). Differentiated from Black Opal, which has a dark background colour.
Wood Opal. Any Opal that formed a pseudomorph after wood from a tree, and retains the original shape and appearance of the wood. Wood Opal may refer to both Common Opal and Precious Opal, but the term usually refers to large pieces of
Common Opal.
Yowah Nut. Small, rounded form of Boulder Opal from Yowah (Queensland), Australia in a nodules embedded in ironstone. Closely related to Boulder Opal, it occurs most often as walnut-sized ironstone nodules containing pockets, veining, or
sprinklings of vivid Precious Opal.
This is not a comprehensive list of opal types as more are being found, but is as complete as we can make it, at this time.
We hope that you have enjoyed this booklet and continue to enjoy the beauty of one of natures gifts.
Glossary of Terms:
Amorphous. Shapeless. Not consisting of crystals. Non-crystalline. Glass is amorphous. Sugar is crystalline.
Deflection. The bending of rays of light from a straight line.
Diffraction. The Breaking up of a ray of light into either a series of light and dark bands or into coloured bands of the spectrum.
Diffuse. To spread out so as to cover a larger space or surface. To scatter.
Fluorescent. A light produced by the electrical stimulation of a gas or vapour. Fluorescent lights have a similar effect on opal as a bright cloudy day--they do not properly bring out the colours in opal .
Hydrate. A compound produced when certain substances chemically combine with water.
Incandescent. Glowing with heat (red or white-hot) as in a light bulb which glows white hot, but produces a light that more closely simulates natural sunlight. Sunlight and incandescent lights bring out the natural colours in opal.
Opal. Opal comes from the Latin word opalus, which means to see a change in colour. Chemically, opal is hydrated silica, similar to quartz.
Opalescence. A play of colour similar to that of an opal
Opaque. Not allowing light to pass through. The opposite of transparent.
Play of Colour. The way in which colours change as an opal is tilted in different directions.
Silica. (Silicon Dioxide) A hard, white or colourless substance, that in the form of quartz, enters into the composition of many rocks and is contained in sponges and certain plants. The needle in the mouth of a female mosquito is made of silica. Flint, sand, chalcedony, and opal are examples of silica in different forms.
Spectrum. The band of colours formed when a beam of white light passes through a prism or by some other means (e.g. mist or spray, in the case of a rainbow) The full range of spectrum colours are: red, orange, yellow, green blue, indigo, and violet.
Sphere. A round three-dimensional geometric shape whose surface is equally distant at all points from the centre point.
Translucent. Letting light through without being transparent.
Transparent. Easily seen through. (Glass like)
General Glossary:
Agate - Fine-grained variegated chalcedony with banded, striped, or moss like coloration.
Amorphous - Having no definite form.
Black Opal - Rare form of mineral opal found only in Australia.
Cabochon - A gem or bead cut in convex form and highly polished but not faceted. Also, this style of cutting.
Crazing - Tiny cracks on the surface.
Crystal Opal - Transparent with flashes. Highly valued due to the brilliance of its colours and the fact that many layers of colour within the stone can also be seen.
Crystalline - Composed of or resembling crystals.
Direction - A measure of opal value.
Dopping - Attaching a gem to a wooden extension by means of adhesive wax in order to polish or facet the stone with greater ease.
Doublet - A manufactured opal gem consisting of two layers: Opal and obsidian or ironstone.
Fire (or pinfire) - A measure of an opal's colour or iridescence.
Fire Opal - A translucent or transparent mineral opal found mainly in Mexico.
Geothermal - Of or relating to the heat of the Earth's interior.
Mohs' Scale - A scale of hardness for minerals in which 1 represents the hardness of talc and 10 (sometimes 15) represents the hardness of diamond.
Organic Opal - An opal formed from the chemical petrifying of organic materials such as wood or seashells.
Potch - Crusty mineral coating on naturally occurring opals.
Quartz - A mineral SiO2, silicon dioxide, that occurs in crystals or crystalline masses.
Silica - A mineral SiO2, silicon dioxide, that occurs in crystalline or amorphous masses.
Synthetic Opal - man-made gem opal.
Triplet - A manufactured opal gem consisting of three layers: Clear quartz, opal, and obsidian or ironstone.
White Opal - common form of gem quality opal, usually white or milky white in colour with bright pinfire flashes.
| Related Auctions |
|
| Related Categories | Coober Pedy Opals, Opalized Fossil, NR Opals, Ethiopian Rough Opals |
| More Articles | Return to Opal Information |
Last Update: 30 Dec 2010