"Crystals grew inside rock like arithmetic flowers... obedience to an absolute geometry."
Anne Dillard, American author
Crystals are solids—like salt, diamond, and quartz— that have their constituent atoms (or molecules) in regular orders. These patterns repeat in all directions. X-rays penetrate solids and are scattered by the clouds of electrons that surround the nuclei of each atom. Because the atomic arrays in crystals are strictly regular, the X-ray scattering is not random. Measuring the intensity of the X-rays in different' directions and the specific angles at which...the scattering occurs enables the separation of the arrays of crystal atoms to be calculated. The study of crystal atom spacing and ordering is known as crystallography. X-rays have wavelengths that are of the same order of magnitude as both the sizes of typical atoms, and also the spacing between solid arrays of atoms.
In 1912 Max von Laue (1879-1960) and Paul Ewald (1888-1985) suggested that the regular arrays of atoms in a crystal might act like the lines on a diffraction grating. Laue shone a beam of X-rays into a sphalerite crystal. Placing a photographic plate behind the crystal he noticed that the scattered X-rays produced a set of circular spot patterns around the larger spot formed by the central beam. He calculated the crystal array separations from the scattering angles.
Since then X-rays have been used to probe metals, chemicals, and biological samples. Huge advances have been made in the fields of organometallic and supramolecular chemistry. Dorothy Hodgkin used X- ray crystallography to calculate the atomic structure of such things as cholesterol, vitamin Bu, penicillin, and insulin. X-rays are widely used today in the pharmaceutical industry.
