Opals : Mine to Market – Matthew Hopkins

Matthew Hopkins discussed the early Australian mines, mining processes and the stages opal goes through to get from mine to market. Matthew Hopkins is a partner in Hopkins Opal, a family mining, cutting, jewelry design, and wholesale distributor dealing in high quality Australian Opals. Miners, cutters and wholesalers of fine quality Lightning Ridge black opal.

Opals are the product of seasonal rains that drench the dry ground in an arid places, such as Australia’s outback. The water soaks in and penetrates deep, carrying silica with it. Then, the water evaporates during a dry spell, leaving silica deposits behind forming opals.

No two opals look the same, and the play of color for each precious opal is different, giving them wide-ranging appeal. Common opal has a milky, dull color, while precious opal displays a wide range of color which makes it so valued.

Opal is a noncrystalline form of the mineral silica which, despite its amorphous structure, displays an amazing degree of internal organization. Opal is related to its more commonly found but highly crystalline cousins quartz and agate, and is formed from amorphous “balls” or lumps” of silica rather that from ordered, naturally growing crystals. Opal bearing ground is specifically searched for by opal miners.

Most of the world’s gem quality opal comes from Southern Australia, although it can be found in other parts of the world such as Brazil, Mexico, Hungry, Peru, Czechoslovakia, Nevada, Honduras, or from Ethiopia (in the last 10 years).

Most black opals come from Australia, but recent finds in Ethiopia have resulted in Black Opal. Ethiopian Opals are of from volcanic (Hydrophanic) activities. Regardsless of the origin, opals are unique and no two are exactly alike, as they come in various shapes, colors and qualities.

Fire is a nomenclature for color in opal, but the name Fire Opal is for a specific type of Mexican opal. Brazil has sedimentary opal similar to Australia. Peruvian opal is used a lot by designers as it is often a bright blue. Hungarian opal (white opal with little color) dates back to Roman times and was the only marketable opal prior to the opening of mines in Australia. Pre-1870 opal was likely Hungarian opal, so early Victorian or Georgian pieces would have had Hungarian opal. Hungarian opal is no longer actively mined.

Here are some definitions to help you in identifying each type of precious opal:

Natural Opal: A natural opal is a stone which has not been changed from its natural state in any way except to be fashioned into a gemstone through cutting and polishing.

Treated Opal: A treated opal has had some foreign material introduced into the stone. Unusually the treatment is a dye used to darken the opal (Ethiopia). Increasingly, treatments are being developed to stabilize an opal that has cracked or might crack in the future. Treated opal often seen as treated Andamooka Opal has a whitish back ground a little light, uses heated lactose and acid to carbonize the opal in order to help saturate the color making it more noticeable.

Synthetic Opal: Man-made or artificial opal grown in a laboratory and often found on silver jewelry. These opals may be sold under names like Synthetic Opal, Gilson Opal, beside Gilson there are also several other manufacturers, Inamori or Kyocera Opal (Japanese manufacturer), as well as several unspecified Russian and Chinese manufacturers. These opals may also be termed opal imitations since they have a slightly different composition than their natural opal counterpart (they lack the water content usually found in natural opal and may contain some plastic or silica compounds used to cement the silica spheres in stead of the natural water). Although created in a laboratory, these synthetic opals are often difficult to identify without laboratory tests. But there are some clues, First, if the stone has an extraordinarily bright play of color, it may be a synthetic. Next look at the pattern, as most synthetics have an overly regular pattern that looks too consistent to be natural. Synthetics also have a roundish globular (snakeskin) pattern. From the side view, high domed stones will frequently show the play of color in columns going from the top to the bottom of the stone. None of these characteristics prove that the stone is a synthetic, but taken in combination they should make you very suspicious. The Gilson Company, which produces most synthetic opals, has changed its process to produce more natural patterns. The snakeskin pattern is gone. This has made it increasingly difficult to determine when a stone is a synthetic by visual inspection.

Opal Simulates: Opal simulates are man-made materials that have the general appearance of opals-including a play of color in some cases-but are made of a different material that the silica balls of natural opal, or have significant amounts of non-silica such as plastic.

Assembled Opal: Doublets & Triplets are partially man-made stones, consisting of only a paper-thin slice of opal cemented to a black backing. Triplets have, in addition to this, a clear quartz or glass capping over the top to magnify the color, protect the opal, and give it a cabochon (domed) appearance. The idea of doublets and triplets is to imitate valuable black opals at a fraction of the cost.


Opal Doublet


Opal Triplet

Classification or nomenclature of natural opal has three (3) categories Type 1, Type 2, and type 3, which are defined below:

Type 1 – Commonly known as SOLID opal. A single piece of opal with a more or less homogeneous chemical composition. However some parts of the piece may be precious opal and others may be potch and it still may contain minor remains and inclusions of sandstone and other non-opal materials. Solid Opal is formed from a single piece of material, and is the most valuable.

Type 2 – Commonly known as BOULDER opal. A layer of opal that is still naturally attached to the host sedimentary rock in which it was formed (e.g. ironstone or any other rock material). The reason for this is that the layer of opal is usually too thin to be cut from the backing of host rock it was found in. Yowah nuts were found in the far South Western mines at Yowah in Queensland, Yowah nuts are ironstone concretions resembling ‘nuts’ which contain precious opal in their center. Upon cracking or slicing the Yowah nut, the precious opal is revealed inside.

Type 3 – Commonly known as MATRIX opal. The material consists of a conglomerate of minute grains of opal which are diffused as fillings in pores or holes or between grains of the host rock in which they were naturally formed (e.g. Andamooka Matrix Opal). Andamooka Matrix Opal may or may not be treated. If treated it is typically treated in a heated sugar solution and then in sulfuric acid to intensify the color, creating a dark or black background in the opal.

Also Type 3 can be a BOULDER MATRIX which is a special form of matrix opal with a different structure compared to the granular build-up of Andamooka Matrix Opal. It usually shows many fine veins and small patches of opal surrounded by the host rock.
Lightning Ridge is a mining town discovered in 1900 in New South Wales, which is the most important source of the famous Black Opal. Black Opal is a solid gemstone with rare, dark body tone that often feature an impressive play of color. These precious opals are highly valued. A black opal’s base is generally black, dark blue, dark green, or a deep gray, but sometimes can feature a whole rainbow of colors. Buyers can also find semi-black and black crystals which often display a light gray background, which is equally rare.

  • Matthew shared the following book list on opals:
  • Opal Identification and Value, Dr Paul Downing
  • Rediscover Opals in Australia, Stephen Aracic
  • Beautiful Opals series, Len Cram
  • The World of Opals, Allan Eckert 
  • Opals, Fred Ward
  • The Opal Book, Frank Leechman

In Conclusion:
Australian opals are regaining popularity worldwide.
Strong demand for opals from jewelers and designers for one-of-a-kind custom jewelry.
Production decline from the source.
Demand increases strong and steady.
High-end Australian black opal as investment possibilities.

DCGIA Thanks Matthew for sharing with us!

Summary by Charles Marts

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