We have all heard of crystals, but did you know that our company has a crystallographer, Irena Petrović Prelević? She is the chief specialist in mineralogical research at the Rock Testing Department of the Upstream Laboratory in the Scientific and Technological Center. 

Crystallography is an interdisciplinary science that utilises knowledge from various fundamental sciences, such as physics, chemistry, physical chemistry, mathematics, and mineralogy, to examine the structure of a crystalline material—specifically, how atoms are arranged and what types of bonds they form within that crystalline substance.

• For NIS, crystallography is very important from a geological perspective. Here, we primarily examine the mineral composition of extracted drilled rock material. We determine the mineralogical composition of the entire sample, as well as the clay minerals, which are particularly significant in this field but are also specific and have a characteristic structure. We also analyse the deposits that inevitably form in the equipment. For example, if a certain material accumulates in a pump, our colleagues bring us a sample, we examine it, and identify the material. Then they know exactly what to use to remove it and get the facility back up and running, Irena explains.

The information obtained by the crystallographer through the processing of collected materials is important, for example, to colleagues in petrophysics and reservoir research, as they use the data to put together a larger puzzle.

• The rock material arrives to us in a powder form, which is then placed under light pressure into a sample holder. This prepared sample is placed in a diffractometer, where X-ray beams from an X-ray tube hit the sample, get diffracted, and are recorded in a pulse counter. The analysis takes about ten minutes, after which we obtain a result—a diffractogram. But that is not the end, as a detailed analysis of the diffractogram follows, where each peak is assigned to a specific phase. Based on the intensity of the peaks of a given phase, its presence in the sample is determined. This is the result that our colleagues need here, the crystallographer explains.

Before joining the Scientific and Technological Centre, where she has been employed since 2018, Irena worked as an assistant at the Faculty of Mining and Geology. She was also a visiting research associate at the Institute of Chemistry and Biochemistry at Ernst Moritz Arndt University in Greifswald and the Department of Gemstone Research at Johannes Gutenberg University in Mainz.

She used to examine margarine and elephant tusks

Throughout her career, she has also worked on Roman ceramics for archaeological studies, researched margarine, and analysed dental material from the tusks of desert and rainforest elephants. This is the best evidence of the wide applicability of this science.

• We all know about graphite and diamond—graphite is of dark colour, opaque, and quite soft, whereas diamond is transparent, extremely hard, the hardest existing mineral. Essentially, both are carbon, just carbon and nothing more, but the carbon atoms are arranged differently in their structures. In diamond, we have shorter and stronger bonds, while in graphite, there is a layered structure. When we write and when graphite leaves its mark on paper, it is, actually, the weak bonds between layers being broken. This is why crystallography is so important, as it shows how the characteristics of a solid material vary depending on how the atoms are arranged, our interviewee emphasizes.

There is another example that is more interesting and even sweeter

• For example—chocolate. Cocoa butter is the main ingredient in chocolate, and it can crystallize in six different forms. However, only one of these forms melts slowly in the mouth and has a pleasant taste, though it is not very stable. After some time and at elevated temperatures, it transitions to another form. We have all experienced when chocolate develops a white bloom and feels gritty in the mouth as some small grains of sand. Fortunately, this transition from one form to another is not very quick, so we have the chance to enjoy the chocolate before that happens, Irena explained.

Some interesting examples of crystalline forms

• The chemical compound silicon dioxide, the primary component of sand, occurs in nature in eight crystal forms (polymorphs), with quartz being the most common. All of these forms, of course, have different properties. However, silicon dioxide also appears in several non-crystalline, amorphous forms, where the disordered arrangement of atoms is responsible for the properties of glass, says Irena.

Another example is calcium carbonate, commonly known as limestone, which is also very prevalent in our world. It crystallises as calcite, aragonite, and vaterite. Each of these forms has very different diffractograms, making them easily identifiable by X-rays and crystallography. This is crucial because if you tell someone that calcium carbonate in a sample is present as aragonite, they will know that the sample formed under high pressure, along with many other details that would otherwise remain unknown.