Peyton Beals, Geology Consultant
As a complete digression from this article, I was disheartened to learn of Dr. Robert Duncan-Enzmann’s passing on October 19, 2020. I regret that I never had the opportunity to meet with Dr. Enzmann personally. The Enzmann Archive materials indicate that he was an individual of immense intellectual capacity and the possessor of both broad and deep concepts that span from paleolithic languages to interstellar starship design. Until there is no further reason to do so, I will continue to research the works of Dr. Enzmann and attempt to promote and distribute his knowledge.
In this installment, I will focus on one of Dr. Enzmann’s professional projects that may provide an appropriate segue from my previous offering. Dr. Enzmann was involved in an effort with the title of the Synthetic Pegmatite Project. The definition of a pegmatite will be detailed later, but this interest in human manipulation of geologic processes could explain Dr. Enzmann’s interest in the creation and production of synthetic gems (cubic zirconia) that I covered in my last article (ENDEAVOR #6). Both activities indicate a desire to understand and control the natural forces necessary in the formation of rocks and minerals.
During the latter half of the 20th century, scientists and entrepreneurs sought to create and fabricate valuable materials that included emeralds, topaz, and diamonds. For whatever reason, Russian scientists appeared to lead in this activity. Russian scientists were the first to synthesize cubic zirconia, and they were also the first to create synthetic diamonds. At that time and even unto the present day, the energy required to accomplish the desired results often exceeds the eventual product’s value. Apart from cubic zirconia (which is not a naturally occurring gem), the quality of synthetic gems has seldom achieved the standards established by agreed-upon mineralogical or gemology criteria.
Pegmatite is an intrusive, igneous rock formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in.). Most pegmatites are found in sheets of rock (dikes and veins) near large masses of igneous rocks known as batholiths. Batholiths are thought to result from lighter crustal material rising after being melted within subduction zones at tectonic plate boundaries. Most pegmatites are composed of quartz, feldspar, and mica, having a silica content similar to granite. Rarer intermediate composition and mafic (rich in iron and magnesium) pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene, feldspathoids, and other unusual minerals also occur. They are found in recrystallized zones and fissures associated with large, layered, ferromagnesian igneous intrusions (also batholiths).
Pegmatites are of both academic and economic interests. Academically, pegmatites represent complex geologic zones that can exhibit extraordinary properties instructive in the formation of rocks, minerals, landmasses, structural geology, and geomorphology. Economically, pegmatites are the source of valuable minerals, gems, and precious metals.
Except for diamonds, almost all other precious gems are found in pegmatitic zones. It is thought that these gems are crystallized in situ within the pegmatitic zone in a process that, while much more involved, is not that dissimilar from the popular science fair project of growing sugar rock crystals in our kitchens. In contrast, diamonds are expelled from regions in, or near, the earth’s mantle through gaseous and explosive volcanic eruptions that manifest as the famous Kimberlite pipes. Gold and silver veins are often associated with hydrothermal deposits that reside within and at the boundaries of pegmatitic zones.
The primary issues of recreating pegmatite conditions are the original starting materials, temperature, and pressure. The problems presented are not dissimilar to those involved in the creation of synthetic diamonds except that the starting material for diamonds is always pure carbon. To artificially create a pegmatite, the starting materials (silica, aluminum, sodium, calcium, potassium, iron, etc.) must be heated to high temperatures (>600° C or 1,112° F) and pressurized at very high levels (>1,725 bar or 25,000 psi.). (see Figure 1)
Figure 1. Pressure and temperature relationships between the four major categories of pegmatite classification, MSC-Muscovite, AB-Abyssal, RE-Rare-Element, and MI-Miarolitic (Černý’, 1991).
Once the high temperature and pressure requirements are met, the resulting crystallization is determined by exothermic conditions. That is, the rate and modus of cooling determine the size of the eventual crystals. If the magma, or geologic “liquor,” cools too quickly, vitrification (glass creation) occurs, and large crystals are not possible. Slower cooling results in generating large, sometimes very large crystals. However, this cooling, or curing, may not be an obvious polynomial decay determined by simple thermodynamics. It might occur as a series of stages whereby temperatures and pressures are maintained, at relatively constant conditions, for protracted periods.
The above explanation is an oversimplification of an extremely complex geologic process to which hundreds of technical papers have been devoted. Other variables in the formation of pegmatites are the water and carbon dioxide content in the magma melt. The presence of both water and carbon dioxide are believed to be necessary to promote ionic migration (to promulgate mineral crystallization) and moderate the cooling process. Modern capabilities make the temperature and pressure requirements achievable. Still, it remains challenging to simulate the exothermic conditions provided by hundreds of feet of insulating country rock and the mass of the igneous intrusion.
One of Dr. Enzmann’s lifelong interests was the mineral beryl (also expressed as the gems emerald and topaz) and the industrially important beryllium metal production. For several years of Dr. Enzmann’s career, he was even employed by the Beryllium Corporation of America. The primary source of high-grade beryl is from crystals and masses formed within pegmatites. Beryllium possesses several beneficial attributes. Relative to most other metals, it is very lightweight while maintaining structural integrity. Compared to some of the other lighter metals (aluminum and magnesium), beryllium has a higher melting point (1,287° C or 2,349° F). It is also an efficient reflector and moderator of neutrons with regard to applications involving nuclear reactions and reactors.
The above factors may contribute to Dr. Enzmann’s vision of interstellar starcraft propelled by nuclear fusion-based (deuterium/tritium) engine designs. Such ships would require strong, lightweight construction materials that are reasonably immune to high temperatures and resistant to deterioration resulting from radiation exposure. For example, the International Thermonuclear Experimental (fusion) Reactor (ITER) Tokamak incorporates beryllium metal as part of the containment vessel design.
Further, beryllium oxide, a precursor to metallic beryllium, is utilized as an insulator in the construction of magnetron devices. Magnetrons are critical components of radar systems and microwave ovens and are responsible for the generation of electromagnetic energy. This may explain Dr. Enzmann’s career evolution into an expert in radar technology and his eventual employment with the Raytheon Corporation. Perhaps his interest and knowledge of beryllium properties lead to this transition in his professional path. A brief conversation with Dr. Enzmann would have confirmed this supposition, but that is, unfortunately, no longer a possibility.
As best as can be discerned from the Enzmann Archive, Dr. Enzmann became involved in the Synthetic Pegmatite Project sometime during 1958 while employed by the Beryllium Corporation of America. However, correspondence and reports contained within the Archive suggest that the Synthetic Pegmatite Project was a joint effort that included the Radio Corporation of America (RCA), General Electric, Boston University, and perhaps other organizations.
Figure 2 Beryllium extraction process
It also appears that the title of the project was a bit of a misnomer. A document in Dr. Enzmann’s handwriting indicates that the project intended to extend and improve the Kawecki and Copaux process of concentrating and beneficiating beryl ores. It was less about simulating pegmatite formation and more about adopting known pegmatite conditions to aid in the purification of beryllium ore and produce pure beryllium oxide and beryllium metal.
The details of the numerous physical and chemical steps required to extract pure beryl, beryllium oxide, and beryllium metal from ores (typically, bertrandite pegmatite) are beyond the scope of this article (see Figure 2).
Suffice it to say that the process is labor-intensive, tedious, expensive, and even dangerous since beryllium (dust) is toxic. Any reduction in these activities would represent significant safety and economic benefits.
Again, as best as can be determined from examining the materials in The Enzmann Archive, Dr. Enzmann’s approach to the purification process was to remove several chemical modifications involving both acids and bases while also eliminating some of the necessary physical filtrations. In essence, Dr. Enzmann intended to “squeeze” impurities out of the crushed ore by employing pressures and temperatures that approached those that existed during the original creation of the bertrandite pegmatite. He then hoped to migrate any impurities away from the high purity beryllium material. A loose analogy to this would be the re-smelting of scrap metals and allowing impurities to “slag off,” thus recapitulating the original metal production. It seems that Dr. Enzmann’s concept was to return the beryllium ore to an earlier physical state that could then be manipulated to advantage. The ultimate result was to produce a billet of beryllium oxide with superficial mineral impurities that could be machined away.
Dr. Enzmann described this technique of hot-pressing materials. One to ten kilograms (2.2 to 22 pounds) of finely crushed (0.85 microns) ore were placed in the correct sized graphite sleeves. Graphite plungers were inserted into both ends of the sleeve to contain the material. The pressure was applied to the plungers employing a hydraulic press. The material was then heated through the graphite sleeve by employing an electrical induction coil. The samples were heated to temperatures of 1,500-2,500° C (2,730-4,530° F) for 4 to 10 hours under pressures of 60-100 kg/cm2 (850-1,425 psi.). After this was accomplished, the samples were further cured in a kiln at temperatures of 1,000-3,000° C (1,830-5,435° F) to drive off (calcinate) additional impurities.
The Enzmann Archive contains both physical and photographic results from the Synthetic Pegmatite Project. During my inventory of the geologic materials in the Enzmann archives, several examples of “thin section” samples were uncovered. These were the size of a microscopic slide. Also found in The Archive were semicircular samples that gave the appearance of porcelain. They were mostly of an off-white, cream color that, sometimes, possessed small dark inclusions. Having already reviewed the Synthetic Pegmatite Project documents, I was able to make the relatively obvious correlation between these samples and the project. The various papers and reports associated with the project also include crystallographic and photographic evidence of the results.
Since pegmatites’ primary characteristic is crystal growth, I was initially surprised by the lack of large crystals observed in the thin sections and photographs. I assumed that the experiments had “failed” due to the absence of apparent crystallization. It was only after further research that I began to realize that the goal of the project was to produce a single, monolithic crystal of beryllium oxide, of extremely high purity, with virtually no inclusions. I am, by no means, certain of this speculation. Still, it appears to be supported by the copious notes made by Dr. Enzmann regarding the formation and location of the darker ferromagnesian impurities.
He seemed intent on understanding how to migrate these impurities to the edges of the experimental samples. Figure 3 is an example of what I believe to be an experimental success (on the left) and two less encouraging samples (to the right).
Figure 3 Beryllium
A perusal of modern beryllium ore processing indicates that Dr. Enzmann’s approach has not been adopted entirely. However, aspects of the Synthetic Pegmatite Project can be found in current techniques. The process of ‘hot-pressing” is utilized to create beryllium metal billets of the highest purity.
Once again, I have ventured into the mind and accomplishments of Dr. Robert Duncan-Enzmann. I am consistently impressed by his distinctive combination of a creative and adventurous approach to futuristic concepts meanwhile maintaining a high degree of attention to detail. Though the Synthetic Pegmatite Project may have been only marginally successful, it is another example of Dr. Enzmann’s desire to expand human knowledge in the natural sciences.
Figure 4 is a close-up of the final product, which is a billet of pure beryllium.
It is possible, even probable, that the pressures described in the experiments were insufficient to obtain the desired results. It is conceivable that with more modern and competent hydraulic apparatus (diamond press), Dr. Enzmann’s goals could have been achieved.
Ultimately, I feel that The Synthetic Pegmatite Project was both economically and academically interesting to Dr. Enzmann. Certainly, since he was employed by the Beryllium Corporation at the time, there was a compelling economic aspect to the endeavor. However, Dr. Enzmann appears to never allow an opportunity to pass in which he can accumulate additional knowledge. His notes concerning the project suggest that he also intended to prepare and submit a scientific paper on the effort. As always, I will continue to delve into The Archives in search of such items.
- From GreatMining.com/mining/MetalsInfo/Beryllium.
- Kjellgren, Bengt R. F., Status of the Beryllium Industry in the United States of America.