Classification of gemstones

Classification of gemstones.

Unlike the colorless ones, colored stones can be divided into two groups: chemical compounds on its own, solid color, independent or only slightly dependent on impurities, and compounds of variable color, depending on the content of additional ingredients. The first group includes e.g.. malachite - one of the copper ores. The second group is already known to us: korund, beryllium compounds and quartz. In a clean state, colorless without any additives. Their color is therefore foreign-allochromatic (from the Greek words allos – alien and chroma – barwa, Colour), dependent on additional coloring agent, an element or, more commonly, a chemical compound, which we call a chromophore, that is, bearer of color. The same elements or compounds are also the cause of the color of stones belonging to the first group - stones with their own color. There is only one difference. In this group, these compounds are not pollutants, but the main ingredients of gemstones. Malachit, turquoise, lazuryt, chrysocolla and dioptase are copper compounds. Malachite has a characteristic color of malachite green, and the dioptase of emerald green, lapis lazuli blue, and turquoise and chrysocolla greenish-blue in various shades. So, copper is a chromophore that stains green or blue depending on the compound, in which it occurs. Green copper is easy to see on copper sheet roofs or bronze products – an alloy of copper with tin, even on old copper coins. As a result of the corrosive influence of the environment, the so-called. malachite green snow.

But the matter is not so simple. Green-colored stones are the most abundant in nature. Green is emerald, several varieties of grenades, actinolite, heliotrop (dark green with red spots), ekanit, some varieties of fluorspar, damantoid, jadeit, aventurine quartz and many others. Meanwhile, e.g.. an emerald with a color almost identical to the emerald color of dioptase does not contain even traces of copper. Thorough research has shown, that the emerald's chromophore is chromium. The same element, more specifically, chromic oxide Cr2O3, colors the ruby ​​red. To confuse things even more, nature created emeralds colored green with iron and emeralds, in which the color carrier is vanadium. When trying to synthesize emeralds, it turned out, with the most beautiful emerald color, it is easiest to obtain vanadium.

We know one thing for sure. Chromophores can be and are only metals or their compounds. We know too, that the color may change depending on the amount of impurities. The bright red ruby ​​changes its color to the darker one, the more chromium oxide it contains. The blue color of sapphire is the result of titanium contamination. Iron stains green from light to dark green, bluish, and even in black, when it is divalent iron, so such, which forms iron oxide FeO, or in yellow, red in various shades up to brown, when it is trivalent, thus it forms Fe2O3. Dyes are also lithium, cobalt, nickel, gal, through, rubidium and other metals. These are the metals, or more precisely their relationships, they are the dyes of our Earth, they give beauty to gemstones, thanks to them, the artist had a wealth of colors and shades from the earliest times, they beautify the porcelain, glass, our clothes, cars and everything, what is colorful around us, colors.