Various physicists searched for an understanding of the nature of X-radiation. Because the radiation seemed to behave differently from light, he thought it a completely different phenomenon, calling it X-radiation. Röntgen deduced that electrons interacting with the walls of the tube produced a high-energy form of radiation, and he showed that the radiation could penetrate paper and even thin metals. By chance, he observed that a nearby piece of barium platinocyanide fluoresced when he turned on the tube. He was studying the relationship between matter and force as charged particles flowed from a heated filament in an evacuated glass tube. Röntgen taught and studied physics at the University of Würzburg in Germany. All this knowledge would have been unobtainable if Röntgen and his coworkers had not recognized the importance of some curious phenomena they observed while studying cathode ray tubes (early versions of television tubes) in 1895. We draw pictures, make enlarged models, and study the details of crystal structures of thousands of minerals. Today we accept without question the idea that atoms bond together in regular arrangements to make crystals. In less than two decades, scientists developed a firm theoretical basis for understanding how atoms are arranged in minerals. Mineralogists quickly discarded many hypotheses disproved by X-ray studies just as quickly, they developed and tested new ones. Wilhelm Conrad Röntgen’s discovery of X-rays in 1895 allowed mineralogists to proceed with their studies and eventually led to a greater understanding of crystal structures. Without a way to test hypotheses, development of an understanding of atomic arrangement and of bonding in crystals was stalled. Some ideas about crystal structure were generally accepted, while others were poorly understood and hotly debated. They hypothesized about atomic arrangements and the nature of crystal structures, but they lacked direct evidence. By the late nineteenth century, mineralogists knew that crystals had ordered and repetitive crystal structures. Scientists studied minerals for hundreds of years before the discovery of X-rays. Other important analytical techniques include X-ray fluorescence, atomic absorption, inductively coupled plasma mass spectrometry, ion microprobe, Mössbauer spectroscopy, visible and infrared spectroscopy, and Raman spectroscopy.ġ2.1 X-ray Diffraction 12.1.1 The Discovery of X-rays and Diffraction.Electron microprobe data yield mineral compositions based on X-ray intensities.Scanning electron microscopes allow high-magnification imaging of mineral crystals and of thin sections.Single crystal diffraction data allow crystallographers to figure out where atoms are in a unit cell.Compositional variations cause slight variations in X-ray patterns.We use a powdered sample for routine mineral identification.Directions of diffraction tell us the spacings between planes of atoms in a crystal intensities of diffraction tell us the number of atoms on those planes.When X-rays interact with atoms, the rays are scattered in all directions coherent scattering by multiple atoms produces X-ray diffraction.X-rays may have many different wavelengths but for diffraction studies we isolate one.X-radiation, discovered in 1895, was the key to understanding atomic arrangements in crystals.12.1 A powder X-ray diffractometer 12 X-ray Diffraction and Mineral Analysis
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