What is the shine of a mineral?
In the description of stones you can see a description of such properties as hardness, density, syngony and brilliance. At first, for me these description properties were meaningless words that I didn’t pay attention to at all. I think many of you will be interested to know what all the listed properties of minerals are. Not only interesting, but also useful information for the proper use of the mineral. Hardness. The hardness of stones is determined using the Mohs scale. For this purpose, a specially selected series of minerals is taken, which are arranged in order of increasing hardness: talc, gypsum, calcite, fluorspar, apatite, orthoclase, quartz, topaz, corundum, diamond. According to this scale, stones are divided into three groups: The hardness of the rock can be determined even more accurately using the PMT-3 device, the principle of which is to press a diamond pyramid into the sample Hardness 1,2 – scratches with a fingernail. Hardness 3,4, 5 – can be scratched with a knife. Hardness 6 – scratchable with a file. Hardness 7 – machinable. Hardness 8,9 – scratches glass. Hardness 10 – cuts glass. Why is it necessary to know the hardness of purchased minerals or products made from them? For a basic storage rule. For example, the same balls of different minerals with different hardnesses must be stored separately from each other. A quartz ball can easily scratch the surface of a calcite ball. Or when we purchase two balls in order to “sort” them in the palm of our hands, we need to understand that high-hardness balls will be suitable for such purposes. Because balls of low hardness will get scratched very quickly and lose their original appearance. Density. Density is the mass of a substance per unit volume of a body. The density of natural stone directly depends on the composition of minerals and porosity. In general, the higher the density of a mineral, the heavier it will be in weight. Syngony. Syngony is a group of types of symmetry that have one or more identical symmetry elements and have the same arrangement of crystallographic axes. Crystallographic classes, or types of symmetry, are combined into larger groupings called systems or syngonies. There are seven such syngonies: L22P; 3L2; 3L23PC L3; L3C; L33P; L33L2; L33L23PC; L4; L4PC; L44P; L44L2; L44L25PC; Li4; Li42L22P Li6=L3P; Li63L23P=L33L24P; L6; L6PC; L66P; L66L2; L66L27PC 4L33L2; 4L33L23PC; 4L33L2(3Li4)6P; 3L44L36L2; 3L44L36L29PC Highest category Cubic system. The most symmetrical crystals crystallize in this system. In the cubic system there is more than one symmetry axes higher than the second order, i.e. L3 or L4. Cubic crystals must necessarily have four third-order axes (4L3) and, in addition, either three mutually perpendicular fourth-order axes (3L4) or three second-order axes (3L2).
The maximum number of symmetry elements in the cubic system can be expressed by the formula 3L4 4L36L29PC. Crystals of the cubic system are found in the form of a cube octahedron, tetrahedron, rhombic dodecahedron, pentagon-dodecahedron, etc. Average category. Syngonies of the middle category. This group unites crystals that have only one symmetry axis of order higher than the second. The middle category includes hexagonal, tetragonal and trigonal systems. The hexagonal system is characterized by the presence of one sixth-order symmetry axis (L6). The maximum number of symmetry elements can be as follows” L56L27PC. Crystals of the hexagonal system form prisms, pyramids, dipyramids, etc.
Lowest category
- glass (fluorite, plagioclase; in general 70% of all known minerals),
- diamond (diamond, beryl),
- fatty (nepheline, sulfur),
- mother-of-pearl (opal, talc),
- silky (gypsum, hornblende),
- matte lack of shine (bauxite).
The brilliance of a mineral is primarily related to its refractive index. Metallic luster is characteristic of opaque minerals with a refractive index n > 3,0. Semi-metallic luster is observed in opaque minerals with n = 2,6-3,0. Diamond luster is found in minerals with n = 1,9-2,6. For minerals with a glassy luster, n = 1,3-1,9. Other types of shine appear due to the different structure of the surface of minerals.
It should be noted that the same mineral can have different luster depending on the shape of the aggregates and on the cleavage plane along which it is cleaved.
I’ll tell you in my simple language. When we try to describe something, we always resort to similar examples. The same goes for the shine of stones. If it is written that the shine is waxy, then just imagine a polished surface lightly coated with wax. Or, for example, glass glitter. Imagine how shiny the surface of the glass is.
Shine of minerals, an optical effect caused by the reflection of part of the light flux incident on the surface of minerals. The brilliance of a mineral depends on the refractive index and reflectance of the mineral, as well as on the nature of the reflecting surfaces. There are metallic, semi-metallic, or metallic (reminiscent of the shine of tarnished metal surfaces) and non-metallic (group) shines.
Metallic shine. Molybdenite. Mount Vitosha (Bulgaria). Mountain encyclopedia. T. 3. 1987. BRE Archive. Metallic shine. Molybdenite. Mount Vitosha (Bulgaria). Mountain encyclopedia. T. 3. 1987. BRE Archive.
Metallic and semi-metallic luster is characteristic of many opaque minerals: native metals, intermetallic compounds, many sulfides and their analogues (arsenides, selenides, tellurides, etc.), sulfosalts, some oxides, graphite, etc.; inherent in alloys. Non-metallic luster is characteristic mainly of transparent minerals. The most common in the group of non-metallic lusters is glass luster; about 70% of known minerals (quartz, calcite, fluorite, gypsum, celestine, etc.) have it. Some minerals have a bright diamond luster (diamond, zircon, cassiterite, sphalerite, native sulfur – on the faces, etc.). Amorphous metamict minerals have a resinous luster. On planes of very perfect cleavage, light minerals often exhibit a pearlescent luster, due to their layered internal structure (muscovite, talc, etc.). The shine of the same mineral on the edges of crystals and even chips may differ from the shine on a fracture or in aggregates. On conchoidal fractures and other not perfectly smooth surfaces, a greasy or waxy sheen is observed (quartz, native sulfur, nepheline, etc., as well as flints). Cryptocrystalline and fine-grained aggregates often have a dull, matte luster (for example, chalcedony), up to its absence. Mineral aggregates of a parallel-fibrous structure are characterized by a silky shine (chrysotile-asbestos). The luster of minerals is an important diagnostic feature, which makes it possible, together with other features (color, line color, transparency, hardness, density, cleavage, etc.), to distinguish minerals from each other. Pekova Natalya Anatolevna
Published May 23, 2022 at 20:14 (GMT+3). Last updated on May 24, 2022 at 15:47 (GMT+3). Contact the editors
Areas of Expertise: Properties of Minerals
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