The phenomenon of crystallization it is easy to observe on the window glass in winter. When it is warm in the apartment, and outside the window is frosty, really winter weather, steam from a kettle or a pot of soup condenses on a much cooler glass. When there is little frost outside the window, it collects into larger drops and flows down the glass according to the law of gravity. When the glass is very cold – has a freezing point of water, the crystallization process begins on the glass, Ice crystals are born, sometimes forming beautiful ones, flower-like patterns. Sometimes, because the condition for the formation of these patterns is… ordinary dirt, more precisely fine dust particles, which become nucleating agents. When the glass is very, but it's very clean – long arise, Single, ineffective threads, usually arranged in the shape of stars, inside which you could see a dust particle under a microscope. When there are more dust particles - nuclei of crystallization - there are more, many thread crystals are born at the same time. Growing threads go to others, sometimes they cross, most often a thickening is formed at the junction site – a new nucleus of crystallization, and, as a result, the most beautiful designs. Still, however, single ones are visible, clearly formed crystals. "Microcrystalline structure” it arises on the shafts then, when the glass is very dirty, all its surface is covered with dust particles, yes, as in our buses or trams. Crystals form on all these dust particles, but they have no free direction, in which they could grow. After all, there is another embryo right next to it, a new crystal is formed. Only one direction of growth remains – perpendicular to the glass surface. An even skin is formed on the shafts of almost all buses and trams, without any patterns and, in addition, opaque.
Just like the glass covered with microcrystalline ice, all minerals with a cryptocrystalline structure are also opaque, even those made of transparent crystals, as with ice or quartz. The justification for this truth is purely physical, optical character. When a piece of polished metal is rubbed with sandpaper, the metal surface becomes rough, not smooth. Crystalline minerals have a similarly rough surface, and therefore all the gemstones of the chalcedony group. The light falling on such a rough surface is reflected from unevenness in different directions depending on the angle of inclination of the unevenness (the angle of incidence is equal to…), and consequently becomes dispersed. Even if some light penetrates under the surface of a certain number of microcrystals, this will be reflected from the next crystal layer, each of which is oriented differently, hence it also produces a diffuse reflection. This multilayer microcrystalline preserves the opacity of cryptocrystalline minerals, even after the surface is polished. Nevertheless, all minerals, which are to act as a jewel or wall covering, we polish thoroughly. In this way, we reduce the amount of scattered light reflected from the surface, which enables better vision of the color of the mineral.
Among the many varieties of chalcedony, agate is the best known, noblest - chrysoprase, and the most interesting - flamed wood.