In the coming months two doctoral students at the Faculty of Science will be faced with an extraordinary challenge – to find diamonds and describe in detail how they were formed. The task sounds simple, but behind this short sentence is the prospect of hard, painstaking work.
The diamonds these geologists are interested in fall into the 'micro' category. In terms of size their maximum thickness is a third of that of a human hair. It should be added that they appear in rock only thanks to the interplay of very special circumstances.
“It is a hangover from something that happened 340 million years ago," says Jaromír Leichmann, who leads the Brno team of a joint project between the university and the Czech Geological Survey. “The rock went from the Earth's surface to a depth of about 150 kilometres, resulting in its transformation by high pressure, high temperatures and changes in atmosphere, before it returned to the surface."
All that interests Leichmann and his colleagues is the process by which these minerals invisible to the naked eye are formed. Minerals for commercial use in the production of jewellery are the result of an entirely different process.
“Diamonds that reach the Earth's surface as a result of an eruption have much more time to crystallize, so they are larger," explains Jana Kotková, leader of the whole project. Three years ago she found microdiamonds in the Ore Mountains somewhere near Ústí nad Labem. (Fearful of attracting amateur prospectors, she does specify the location.)
Such an amateur search would in any case be pointless. Amateurs would have no chance of telling at a glance whether rock contained microdiamond, nor if such a find was of commercial interest, as microdiamond can be used only as a building stone. “There is no question of mining these diamonds," says Leichmann. “For that to happen each ton of rock must contain at least two tenths of a gram. With microdiamonds we're talking about hundredths and thousandths of a gram."
Painstaking work for scientists
Although microdiamonds have been found in granulite rock formed by small minerals, rather than being open to view they are hidden within other minerals. Scientists suspected they were in the granulite but it was difficult to find them even under a microscope. “It's like searching the night sky," says Jana Kotková. “I succeeded in confirming some of dozens of inclusions as diamonds on the first day I used special apparatus, after weeks spent at the microscope. My colleague in Greece had to work hard at it for a whole year."
The making of such a search is the task of the two doctoral students. Petra Jakubová will search thin slices of granulite for more diamonds, whose structure she will examine, while Jakub Haifler will focus on the processes that brought about their formation.
As scientists know, the formation of such valuable stone requires carbon – in the case of microdiamonds, this can come from the Earth's crust or mantle – and high pressure and temperatures. Everything occurs at great depth.
How exactly is the mineral formed? This remains to be ascertained; so far only theoretical models exist. Other things, too, must be determined, such as whether there are exceptional hoards of microdiamonds in other locations of the Czech Republic.
Clarification of processes by which microdiamonds were formed will bring us closer to phenomena hundreds of millions of years old. It may also help us understand the present.
“By reaching an understanding of these phenomena we will discover more about the origins of earthquakes," says Leichmann, before referring specifically to the Himalayas. The earthquakes that occur there today mean that something is going on far below the mountains that will bring about the formation of microdiamonds. It follows from this that in the vicinity of these minerals invisible to the naked eye there was once a mountain range just as high as the famous massif in Asia.