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Chapter 1   Page 12 Man Made Quartz Crystals THE NATURE and general chemistry of hydrothermal vein quartz is well enough known to allow man to mimic the processes. This was first done in the research laboratory, and since the middle 1950's, by industry. Large stainless steel tubes or as they are called "pressure bombs" are partially filled with a high purity quartz termed lasca. Lasca is the chemical feedstock and the source of silica in the artificial system. Then water is added. Suspended in the upper half of the vertical bomb are wafers of quartz called seed crystals. A cap is screwed on and the bomb suspended vertically. The lower one-half being inserted into an industrial furnace. The heated fluid dissolves the lasca, rises by convection, cools and deposits the dissolved silica on the seed wafers, and then is displaced by more heated silica-saturated fluid. Crystal growth is monitored by passing x-rays through the upper portion of the pressure bomb and examining the size of the growing crystals. Growth must be uniform and constant so the temperature of the furnace and room are critically controlled. At the end of a typical run of two weeks, the bomb is allowed to slowly cool and then opened and the finished crystals are removed. The top example in the photo below is about seven inches long. ted-lind@mediaone.net The following information is furnished by Ted Lind, an engineer with Motorola, who has several years experience in the commercial growth of quartz. My thanks to Ted for furnishing this write up. I have made no changes to either his or my own article, so the reader can discover that sometimes even I need help! Synthetic Quartz Mike, I read the article you wrote for Rockhounding Arkansas concerning the growth of synthetic quartz. Since this is a subject I know a little about, I thought I would provide some information on how these crystals are grown commercially. The vessels are usually not stainless steel. They are an iron alloy that is specially treated when made. I don't remember the designation of the alloy, but could find out if you are interested. There is an interesting step in the fabrication of the vessels that is a result of the operating pressures used. Autoclaves have operating pressures between 10,000 psi and 40,000 psi, depending upon the chemistry of the process used. Because of these high pressures, the material used is heat and pressure treated to provide a very dense matrix. One step in the process (of manufacture) is to take the whole autoclave and put it into a bigger autoclave (vessel) where the temperature is raised to around 3500 decrees C. and the outer autoclave is pressurized with something like 60 atmospheres of argon. This step is done to force any voids, bubbles, or defects out of the structure. The wall of a small commercial autoclave would be around 3" thick. The cap to the autoclave resembles the breech plug of a naval cannon. There is usually a very special sealing arrangement required to withstand the high pressures developed in an operating autoclave. When the vessel is put into service, the manufacturer performs a 'conditioning' run which allows a crystalling coating to form on the inside of the vessel. This coating is stable and prevents interaction between the vessel and the chemical solution used in the vessel. We use Lascas from Arkansas. The material is milled to a uniform size, approximately 1" to 1.5" in diameter, cleaned, and etched. The solute used in the autoclave is only partly water. Either a sodium hydroxide or sodium carbonate solute is used. The quartz and the solute nearly fill the vessel when it is closed. This is one of the reasons the high pressures are developed since water is basically incompressible. While x-rays have been used in the laboratory, they are not generally used in a production operation. The growth process has to be well understood and is allowed to proceed under very controlled conditions. Often a computer is used to run the autoclave during the 30- to 120-day growth cycle. (Time is a function of the size of the stone being grown.) it is very possible to predict quite exactly the point at which the growth process needs to be terminated. Usually the grown stones will have less than 1/4 of an inch between them at the end of the cycle. Heating of the autoclave is accomplished by means of electric heaters fastened to the outside of the vessel. There are heaters throughout the length of the vessel with a higher density at the bottom. The temperature of both the bottom dissolving zone and the top growing zone has to be carefully controlled. A baffle is situated between the two zones. This baffle allows the bottom temperature and the top temperature to be significantly different and to help each zone have an isothermal characteristic. The baffle also restricts the convection flow and channels the convection flow into a desirable geometry. Around the autoclave and the heaters there is an exterior insulation package. This insulates the autoclave and helps isolate it from external temperature changes. There is usually an air space between the insulation package and the vessel. There are also vents at strategic places to allow the air flow to be controlled. Changing these vents and the power delivered to the heaters determine the thermodynamic condition of the autoclave. The main parameters that are monitored in the process is the temperature at various points on the vessel and the pressure of the vessel. These parameters are used to control the growth process. They have to vary during the process because at startup the majority of the quartz material is at the bottom of the autoclave. The top only contains the seed material. At the end of the process, most of the quartz in the bottom has dissolved and recrystallized on the stones in the upper growth zone. As you can imagine, moving this much material around greatly affects the hydrothermal flow conditions and the thermodynamic state of the vessel. For this reason, the control algorithms are designed to make continual changes during the process to compensate for these changing conditions. In laboratories, they use smaller autoclaves for experimental work. I suspect your description really describes a lab operation. A two week growth cycle would be very short for any commercial operation. Commercial autoclaves range from 10" in diameter x 10-15' long to 1 meter (> 3 ') and nearly 12 meters (over 32 ') high. Companies that grow quartz may have as few as 20 autoclaves to several hundred vessels. ToyoCom was growing gem-like quartz crystals over ten years ago. They add impurities to the growing solution to provide color to the quartz. I have a tie clip with a quartz gem that looks like a diamond with a very light blue tint. It is really quite nice. [My appreciation to Ted Lind, recently retired from Component Technology Laboratory, for his write up! He is willing to answer questions at: TLind@mediaone.net] Read more about synthetic quartz and man-made gemstones with books from Amazon.com Simon and Schuster's Guide to Gems and Precious Stones C. Ciprianai, et al / Paperback / Published 1986 Synthetic, Imitation and Treated Gemstones Michael O'Donoghue / Paperback / Published 1997 A guide to man-made gemstones Michael O'Donoghue/ Published 1983 Man-Made Gemstones D Elwell / Published 1979 Synthetic gem and allied crystal manufacture Daniel MacInnes Synthetic gem materials Michael O'Donoghue Synthetic Gems, Production Techniques Vol 149 Lee Yaverbaum / Published 1980   Ch 1, Page 12 Contact Mike and Darcy Howard, the authors of Rockhounding Arkansas Revised April 2000 ©Rockhounding Arkansas 1998 http://rockhoundingAR.com