Immortal minerals

26 June 2012

The Mineralogical Collection of the Institute of Geosciences is housed in a simple room with 60s charm. Here, rubies, emeralds, gold, and much more sparkle in plain glass cabinets. Professor Dr. Wolfgang Hofmeister guards these treasures and is responsible for adding new items – sometimes even vaporizing a diamond in the service of science.

The diamonds tumble onto the tabletop. "Dresden Green," says Professor Dr. Wolfgang Hofmeister with a grin, as he unwraps one stone after another from its paper. "Blue Hope, Tiffany." Bright blue and warm yellow join the delicate green. "Heart of Eternity, Great Mogul." Behind every name is a story, a legend. "Here, take it," says Hofmeister, offering the Taylor-Burton diamond, a crystal-clear, drop-shaped gemstone. It lies surprisingly heavy in the hand as its facets twinkle in the sunlight. "A colorless diamond – not particularly interesting. It's just carbon atoms arranged in a particular structure; no fun at all."

The Dean of the Faculty 09: Chemistry, Pharmaceutical Sciences, and Geosciences and Director of the Division of Gemstone Research at Johannes Gutenberg University Mainz (JGU) has opened his treasure chamber, which contains the Mineralogical Collection on the fourth floor of the building at Johann-Joachim-Becher-Weg 21. "This room is CCTV monitored" warns a sign at the entrance.

Diamonds for the City of Science

The glass cabinets showcase their treasures on mouse-gray linoleum in a space the size of a living room. There is a sorry-looking potted plant on the window sill, with drooping brown leaves. "I actually watered it today," says Hofmeister in self-defense. However, we are not here to talk about plants, but about the Collection. "The only thing that minerals do is not die; they grow and grow," explains Hofmeister.

But back to the diamonds on the tabletop – which are not at all what they seem. When Mainz was named City of Science in 2011, Hofmeister had them made. They were one of the attractions of the Spektrale exhibition in the Rheingoldhalle. In fact, these fine pieces are made of zirconium oxide. This doesn't make them particularly cheap – it was expensive enough to give them the correct cut. But people have been frequently fooled into believing such gems are genuine. "Sadly, there are always those who are only too willing to sell forgeries to the unwary," says the professor.

Emeralds in raw state

Then he shows us a genuine diamond. It is decidedly smaller at only four carats, but is all the more interesting to researchers. Inclusions provide information and tell the story of the mineral and its place of origin, while the Taylor-Burton diamond just lies there like a piece of glass, its only saving grace being its association with Hollywood stars of a bygone era.

The Mineralogical Collection also contains many other types of stones, which sparkle blue, red, and gold in the glass cabinets. This diversity is there to be explored. Hofmeister shows us the emerald collection which he recently acquired. The funding was provided by the Institute of Gemstone Research in Idar-Oberstein. The green emeralds are embedded in a flat stone. This natural state is interesting to the specialist and important for teaching. Students need to know in which environments the precious stones thrive.

Hofmeister opens a small box with cut specimens that are not even the size of a fingernail. "This is a complete collection from deposits from all over the world." This is also important, as inclusions reveal the origin of each stone. Those that come from Columbia are more valuable than those of the same size from Nigeria. "Emeralds were already being mined in Columbia long ago, so it is unlikely that new ones will be found there. But it's only fairly recently that they were discovered in Nigeria." Who knows what may yet come to light there?

Crazy prices for precious stones

Hofmeister goes from stone to stone, cabinet to cabinet, case to case. The Mineralogical Collection was established in 1967 when the building was constructed. However, the collection contains stones from older collections, including some that were collected in the mid-19th century.

So all this must be worth a lot, right? Hofmeister dismisses the notion. "We are not interested in values." And anyway, when it comes to value, tastes differ. The Chinese like green stones, so they are indifferent to the ruby deposits found in their country, blue is popular in India, and colorless stones were once favored in Christian Europe. "The craziest market is America. If there is even a scratch on a stone, it dramatically loses its value."

Gold from Ontario

As far as scientists are concerned, other aspects are much more important. There is a nugget, for example, that was part of a famous gold strike in Ontario. The solid gold sparkles between quartz and green muscovite. "You'll hardly ever see gold in such a state today." It is usually extracted, melted down and mixed. But who, besides researchers, is interested in the region it comes from?

And here is a sugilite with an extraordinarily intense bright magenta coloration. "But we don't know where the color comes from. We can't find anything. As far as we can tell, it only contains elements that do not produce colors." Yet, the color is there, representing a provocation to and challenge for scientists.

Hofmeister could happily spend all day talking about the Collection. Over here is an amethyst geode that weighs 650 kilos and has outgrowths in the shape of rabbit ears, red rubies from Vietnam glisten, brucite looks like harmless straw but is as nasty as asbestos while a piece of albite is studded all over with tourmaline. "I lectured for a whole hour on that one stone alone," claims Hofmeister.

A diamond is vaporized

But anyone who comes to believe that Hofmeister considers his stones to be sacred better think again. "I have no qualms about pulverizing or vaporizing some gemstones." He has recently done exactly this with a diamond – the process was captured on film. "For fifteen minutes, it glowed red, then yellow, and then it vaporized. After all, it was only made of carbon, it was unstable and had to vaporize in the end. But we wanted to see exactly what would happen."

Meanwhile, Hofmeister packs the Taylor-Burton diamond back in its paper. Thanks to his guided tour, we now know it for the boring thing it really is – crystal clear and not even made of carbon. Just a fake with a nice shine. The Mineralogical Collection has far more exciting things to offer.