The highly regular, and sometimes startlingly angular shape of some well formed crystals can seem eerily out of place in the world of Nature, with its more familiar curving and flowing lines. It's no wonder, then, that a rich history of mystical and mythological lore pre-dates, and coexists with, today's chemical and physical understanding of crystal structure.
Imagine the reaction of our ancestors, so used to the shapes and forms of flowing water, curling fire, gnarled tree branches, curving shell, roseate flowers and sinuous leaves, when they saw something that looks like the images below, perhaps in a mass of rock on a hillside, or upon cracking open an ordinary looking boulder:
The internal regularity that the outer features of such structures implies, was as evident to our ancestors as it is to us, but it was not until the beginnings of modern physics and chemistry (in the 17th - 18th centuries) that some of the underlying causes came to be understood. Full revelation of the most intimate details of crystal formation and properties awaits future generations, but major gains were made in the early 1950's with the advent of a technique called Xray diffraction.
Although definitely more"hi-tech", the principle behind this technique is essentially the same as used in an ordinary medical Xray machine. To illustrate: a beam of Xrays travels through your arm, let's say, to Xray sensitive film below. The dense tissue (bone) absorbs more of the Xrays than does the soft tissue, so the film is exposed differently, and a high contrast picture is made.
In the case of mineral crystals, the dense areas (where atoms are closer together) absorb more Xrays than the less dense ones (where atoms are further apart), and a high contrast picture is produced. For those who have been trained in reading such photos, inner details of crystal structure can be deduced by interpreting the patterns
