The cubic zirconia (CZ) gemstone is a man-made version of the naturally occurring mineral zirconium oxide. The CZ was originally discovered in nature in 1892. Unfortunately, the quantities and size of naturally occurring CZs are such that there is too little naturally occurring cubic zirconia to make it worthwhile to mine the crystals and the naturally occurring crystals are too small.
The process for making cubic zirconia in the laboratory was perfected in Russia by a team of scientists working under V. V. Osiko. Their technique was first published in 1973 and commercial production of cubic zirconia began in 1976. By 1990, annual global production reached 50 million carats. The process for making CZs involves heating a powdered mix including zirconium and a stabilizer in a water cooled crucible. Normally zirconium oxide crystals and not "cubic". The stabilizer agent is added to the powder so that the crystalline structure will be cubic, the same as a diamond. The heat for the crucible is generated by a strong electrical field. The water cooling of the outside of the crucible causes the powder to become heated from the outside in, with a thin layer of un-melted powder on the outside. The material is heated to a very high temperature (about 2,750 degrees centigrade) and pieces of zirconium metal are added to seed the growth of the cubic zirconium crystals. Water cooling is required along with the cooled layer of powder because no known crucible material could withstand this very high temperature. After the crystals are grown at this very high temperature, the crystals are then slowly cooled to 1,400 degrees centigrade and held at that temperature to allow the cubic zirconia to anneal. When this process is completed the resulting crystals are typically 2 inches long and 1 inch wide. These large crystals are cut an polished to make gemstones for use in making jewelry.
Cubic zirconia made by this process is absolutely clear, but can be manufactured in a variety of colors by adding various metals to the powdered zirconium in the manufacturing process. In fact, a blue CZ copy of the Star of India diamond was made to show that this 17th century gemstone was in fact the precursor to what ultimately became the Hope Diamond.
The CZ is so optically close to a diamond that only a highly trained observer can tell the difference. One of the ways that many trained jewelers use to visually distinguish a diamond from a CZ is that a mined diamond almost always has some small trace of color frequently a very light yellow or gray when observed under a loupe. By contract a white or clear CZ will have absolutely no color. Another technique used by jewelers to distinguish a diamond from a CZ is that mined diamonds almost always have small imperfections or inclusions that can be seen using a jeweler's loupe. A CZ does not have these imperfections. A third visual technique for identifying a CZ is that a CZ has more dispersion of light and more prismatic "fire" than a diamond. A fourth way to differentiate a diamond from a CZ is that while a diamond is a better conductor of heat than copper or silver, a CZ is an excellent insulator of heat. Finally, before a stone is set, a CZ can be distinguished from a diamond by the weight and by the thermal conductivity. A CZ will be 1.7 times heavier than a diamond of the same size.
Hardness is also a way to differentiate between a diamond and a CZ. A CZ has a hardness of 8.5 while a diamond has a hardness of 10 on the Mohs hardness scale. A CZ will not scratch a diamond, while another diamond will. This check of hardness is not recommended because it is destructive -- the stone being tested may be damaged. A CZ is harder than most of the gemstones available, but it is not as hard as a ruby, a sapphire, or a diamond.
A CZ is an excellent choice to replace diamonds and colored gemstones in jewelry. The hardness of the CZ makes it harder than dust and therefore perfectly suitable for everyday wear. Optically, a CZ is very hard to distinguish from a diamond. CZs, being man-made are virtually free of occlusions and other imperfections. Finally, cubic zirconia gemstones are very reasonably priced. Where a flawless 1 carat diamond would cost about $4000 or more and a Moissanite simulated diamond the same size would cost about $600, a flawless, grade AAAAA 1 carat CZ could be purchased for less than $10.
Here is a question for people considering a diamond -- given that there are now processes for creating diamonds in the laboratory, might there come a time when the price of diamonds begins to decrease? In 50 years, will people be wearing gemstones that were mined, or will they be wearing gemstones that are chemically identical to mined gemstones, but without the flaws inherent in naturally occurring stones? Does a mined gemstone sound like a good long term investment? While you are considering this, please note that when the Washington Monument in the US Capitol was finished it was capped by the rarest and most expensive metal available at that time. It was capped with about 2 pounds of aluminum. Could the same thing happen to diamonds? The answer is yes it could.
Please select the picture above-right, or select here to view our selection of cubic zirconia diamond simulants.