Types of gemstone brilliance, matte and clear stones, asterism and iridization. Shine and brilliance is the most vivid description of the nature of a gemstone. However, not all gems shine, and the nature of the luster of stones is not as simple and obvious as it may seem. Shall we try to solve one more mystery of the jewelry? The brilliance of a gemstone is its ability to reflect light. It may seem strange, but the luster is totally independent from the color of the stone, but it is directly related to the index of light refraction. Gemstones shine in different ways; the shine typology includes an oily, metallic, pearly, silky, and waxy sheen, but all of them are very rare. A "glassy" sheen is the most common, while a "diamond" sheen, which sparkles and plays the most, is the most prized. Some stones are, however, of a dull or even matt luster. Of course, when it comes to brilliance, the cut plays an even greater role than the natural properties of the gemstone's mineral. The ideal form of the cut that allows us to maximize the sparkle of a gemstone and achieve the ideal total internal reflection is the diamond cut. Only colorless stones that let the light shine through without any distortion can really sparkle. When white light passes through a crystal like this, due to its cut, it is refracted (this is called dispersion), which then decays into a color spectrum, and then literally sprays out a rainbow of colors. Of course, we do not know any stones equal to diamonds in this respect. The iridescent color play of some gemstones is called iridization; the appearance on the surface of stones of light figures in the form of light strips that intersect at one point and resemble star rays is called asterism. The "starry stones" that form such figures are called asterisms. Not only the play of light on its facets depends on the transparency of the stone, but also its price. Precious stones that do not have any visible flaws even under tenfold magnification are extremely valuable. To tell the truth, they are extremely rare, but in most cases, most of them have flaws that are invisible to the eye. Not all of these inclusions spoil the stone; sometimes they make it really unique, such as inclusions of one kind of minerals (a diamond in a diamond) or even foreign ones (zircon in a sapphire). The third kind of inclusions are organic and are characteristic only of amber. Insects, leaves, and other organics "sealed" in amber millions of years ago, all this influences the price of the stone in the most favorable way. In addition to inclusions that change the structure of a gem, all sorts of deformations of the crystal structure of a mineral can be found. They are characterized by colored bands, inclusions, voids and cavities, sometimes filled with liquids and gases.