Beauty, durability, rarity — these are the three main advantages of this gemstone. Representatives of the mineral kingdom that find application in jewelry can be divided into three groups, depending on whether they are transparent, translucent or opaque. The first of these groups is by far the largest and most important, divided into two sections: colorless stones and colored stones. In the first of them, diamond plays a dominant role, because only it has the ability to radiate a wonderful fire and send rays of light at every turn — from sky blue to flaming red, which is especially valued and makes you look for it. Other stones, such as burnt zircon, white sapphire, white topaz, and rock crystal, can also be blinded by the glare of light reflected from their surface or coming from the inside, but not one of them sparkles like a diamond.
It takes all the art of the master to ensure that the facets are positioned in such a way that the richness of the stone is fully revealed. On the other hand, the attractiveness of colored stones depends more on their inherent color shades than on the way they are cut. The tone of coloring should not be too light or too dark: such stones are of little interest. A diamond cutter can, to some extent, correct such defects by making thick plates from some stones and thin plates from others. In some peculiar stones, such as tourmaline, transparency varies greatly in different directions, while in others, such as ruby, sapphire, kunzite, the color changes greatly. The most admirable colors are the fiery red of the ruby, the royal blue of the sapphire, the vibrant green of the emerald and the golden-yellow of the topaz, all of which are pure colors, and the corresponding absorption spectra are generally continuous and often narrow. Therefore, they maintain the purity of their colors even in artificial light, although some sapphires pass relatively much red light and, accordingly, in the evening become purple.
Of the small group of translucent stones that light passes through, but it is not enough to see through the stones, the most important is opal. It and some minerals in this group are valued for the same optical effect that is created on the surface of bubbles, faded steel, etc., rather than for their own coloring. Another type of stone — moon, and stars — reflects light from its inner edges, but not so well as to create a play of light. In the latter group, which unites opaque stones, there are few typical gemstones; the main ones are turquoise, laps lazuli and nephrite. In this case, the light diffuses from the layers directly on the surface of the stone, and the color is determined by the resulting absorption. The dark tone of colored stones is due to another reason: the light entering the stone is completely absorbed by it, and since the light does not come out of the stone, the stone seems to be black.
Of course, it is important that the stones used in jewelry are able to withstand the mechanical and chemical influences that are inevitable in their daily use. Fine particles of sand contained in ordinary dust cause mechanical abrasion, so gemstones should be at least as hard as these particles, a condition that is fulfilled for all major types of stones except opal, turquoise, cryolite, and demand. However, these four stones are only slightly softer than sand particles. Only gemstones that have at least low porosity can be chemically treated during wearing. It is better not to put turquoise in the liquid, even in water, so that the blue-green color does not get a yellowish shade as a result of oxidation. The risk of damaging opals, moon and stellar stones with dirt and grease (if they get inside the stones) is not so great, but it should not be neglected. To an even greater extent, these remarks apply to pearls. Its charm, caused by the special play of light on the surface of pearls, can be lost as a result of contamination with grease, ink or other similar substances; pearls are also very soft.
These are not all the properties of gems on which any of the above classifications are based.