Minerals are determined by the following properties: the color of the mineral and the color of its feature on a porcelain plate, luster, transparency, hardness, cleavage, separation, fracture, magnetism and specific gravity.
Mineral color. The color of minerals is extremely varied and depends on the absorption of some rays of the spectrum and the reflection of unabsorbed rays. Some minerals are characterized by a constant color, for example, magnetite is always black, and malachite is always green. Other minerals have different colors, for example, quartz can be white, yellowish, smoky, pink, purple, black, and sometimes colorless and transparent. Feldspar in granite can be pink, sometimes flesh-red or gray, etc. The colors of minerals are determined in practice by comparing them with well-known, more or less firmly established colors, for example, they say: golden yellow, tin-white, lemon-white. yellow, indigo blue, bottle green, straw yellow, etc. Some transparent minerals have the property of changing color in the same crystal depending on the angle at which they are viewed or depending on the nature of the lighting.
Stroke color. The true color of minerals is well determined in the powder of a crushed sample. To obtain the powder and determine its color, draw an acute angle of the mineral on a white, unglazed porcelain plate or, even simpler, on a fresh broken piece of porcelain. The color of the line does not always match the color of the mineral. Thus, in multi-colored fluorites, the color of the trait of samples of almost black, red and colorless fluorite turns out to be equally colorless. Quartz does not give a line, magnetite gives a black line, multi-colored feldspars - white or colorless, like dark green olivine. The color of the mineral must be observed on fresh surfaces, since the mineral being tested may be covered with deposits of other minerals and, due to weathering, may change color on the surface. In addition, minerals can be covered with “tarnish,” i.e., an iridescent film that changes their true color, which is what we see in Labradorite.
Shine. Most minerals have the ability to reflect light on their surfaces, which explains their shine, which serves as an important diagnostic feature for all minerals. Shine should be studied on fresh fractures, as well as color. The following types of luster of minerals are distinguished:
metallic shine- strong, reminiscent of the shine of a polished metal surface. Minerals with a metallic luster are usually opaque and heavier than others. These include: gold, pyrite (sulfur pyrite), chalcopyrite (copper pyrite), arsenopyrite (arsenic pyrite), galena (lead luster), magnetite (magnetic iron ore), pyrolusite, molybdenite, pyrrhotite, bismuth, stibnite (antimony luster) and etc.
A metallic or semi-metallic luster resembles the luster of metals that has faded over time. Characteristic for graphite, anthracite, rutile, cuprite, hematite, etc.
The shine is non-metallic.Diamond shine- is caused by the reflection of light from the internal surfaces of the mineral and is characteristic of transparent or translucent minerals with a high refractive index. Example: diamond, sphalerite (zinc blende), cinnabar crystals, cerussite (white lead ore), etc.. The latter sometimes has a glassy shine, depending on the angle of incidence of the light.
glass glitter resembles the luster of glass, but is less pronounced than that of minerals with a diamond luster. Many transparent minerals have it. Example: quartz on the faces of rock crystal, calcite, gypsum, olivine (the latter also has a greasy sheen), orthoclase, fluorite, garnet, corundum, etc. . Oily shine resembles a surface greased or oiled. It is characteristic of soft minerals. Example: talc, serpentine, eleolith, nepheline. The latter has a greasy sheen at the fracture, and on the planes of the crystals it is glassy, like quartz, and sulfur, with a greasy sheen at the fracture, has a diamond sheen on the edges. Pearlescent shine with a dimly iridescent iridescent color, similar to the shine of mother-of-pearl, is observed on the cleavage planes and is caused by the reflection of light from the cleavage planes of the mineral. Example: mica, calcite, labradorite. Silky shine- shimmering - due to the fine-fiber structure of the mineral. Example: fibrous gypsum (selenite), asbestos. Malachite has a glassy luster, sometimes up to a diamond-like luster; some fibrous varieties have a silky luster. Wax- low oily sheen to matte. Example: chalcedony.
For dull or dull minerals like bauxite, characterized by a complete absence of any shine. Also lacking shine: chalk, various ocher, sooty pyrolusite. Kaolinite in a continuous mass it is matte, but its individual scales and plates have a pearlescent sheen.
At first, until the geologist has yet developed a “geological eye,” it is difficult for him to discern subtle shades in the color of individual minerals. Different shades of color, as well as shine, are easier to perceive by comparing samples. For example, the straw-yellow color of pyrite in the immediate vicinity of copper pyrite contrasts noticeably with its brass-yellow color.
Transparency. Transparency - the ability to transmit light - is determined by thin fragments of minerals or in plates. According to the degree of transparency, minerals are divided into the following groups: transparent ( rock crystal, rock salt, gypsum, Iceland spar, topaz, etc.), translucent ( chalcedony, opal, beryl, sphalerite, cinnabar, etc.), translucent in the mass ( jade, rhodonite, etc.), translucent at the edges ( feldspars, etc..), opaque ( graphite, magnetite, pyrite, etc..). Except for the last category, all minerals are transparent in thin sections, that is, when examined under a microscope in transmitted light, plates about 0.02 mm thick. Ore minerals are overwhelmingly opaque.
Hardness. Hardness is understood as the degree of resistance of a mineral to scratching, grinding, drilling, pressure, etc. The hardness of minerals is quite varied for different minerals and more or less constant for the same ones, moreover, it is easily and quickly determined. To assess hardness it is accepted Mohs scale , including a list of ten minerals, of which each subsequent one scratches all the previous ones.
There are so many minerals - perhaps this is partly why they are so interesting to collect. On this page you will find a description of experiments that can be carried out without special equipment and thus significantly narrow the search area, as well as a description of the most common minerals, which can be compared with the results of the experiments. You can even go to the descriptions section right now - maybe you will immediately, without any experience, be able to find the answer to your question. For example, in this section you'll learn how to tell real gold from other shiny yellow minerals, read about bands of shiny colored layers in rock, or learn to identify that strange mineral that flakes into sheets when you rub it.
Steps
Part 1
Conducting experiments- You can try to determine what kind of stone it is, or at least determine which of the three types of rock it belongs to.
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Learn to navigate the classification of minerals. There is a place for thousands of minerals on our planet, but many of them are classified as rare or lie too deep underground. Sometimes a couple of experiments are enough, and you are left in no doubt that this is one of the common minerals from the list in the next section. If your mineral doesn't fit any of the descriptions above, try checking your region's mineral classifier. If you have conducted many experiments, but have not been able to reduce the number of options to two or three, search the Internet. Look at photos of each mineral that is similar to yours and look for any tips you can on how to tell the difference between those minerals.
- It is best to include at least one experiment that requires exposure to the mineral, such as a hardness test or a streak test. Experiments that involve only looking and describing may be biased, since different people describe the same minerals in different ways.
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Study the shape and surface of the mineral. The totality of the forms of each mineral and the characteristic features of a group of minerals is called the “general form”. Geologists have many technical terms to describe these characteristics, but usually a general description is sufficient. For example, is your mineral lumpy, rough, or smooth? Is it a mixture of rectangular crystals, or is your specimen bristling with sharp crystalline peaks?
Take a closer look at how your mineral shines. Luster refers to the way a mineral reflects light, and although it is not a scientific test, it can be useful for description. Most minerals have a "glassy" ("glossy") or metallic luster. However, you can describe the luster as “greasy,” “pearly” (a whitish sheen), “matte” (dull, like unglazed ceramic), or any other adjective that seems accurate to you. Use multiple adjectives if you need to .
Pay attention to the color of the mineral. Most people do not see any difficulties in this, but, meanwhile, this experience may turn out to be useless. Small foreign inclusions can cause color changes, which is why you can find the same mineral in different colors. However, if the mineral is an unusual color, say purple, this can significantly narrow the search area.
- When describing minerals, avoid fancy color names like "salmon" or "pussy." Try to stick with just red, black and green.
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Try the stroke experiment. This is a useful and simple test, provided you have a piece of white unglazed porcelain. The back side of tiles from a bath or kitchen is perfect; maybe you can buy something suitable at a home improvement store. Having become the owner of a treasured piece of porcelain, simply rub the mineral on the tile and see what color streak it leaves. Often the color of the streak will be different from the base color of the mineral.
- Glaze gives porcelain and other types of ceramics a glassy (glossy) shine.
- Remember that some minerals do not leave a streak, especially hard minerals (as they are harder than the streak plate).
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Assess the hardness of the material. To quickly determine the hardness of a material, geologists use the Mohs hardness scale, named after its creator. If the result fits the hardness coefficient “4”, but does not reach “5”, it means that the coefficient of your mineral is between “4” and “5”, you can stop the experiment. Try scratching your mineral using the common items mentioned below (or the minerals from the hardness test kit); start at the bottom and, if the test is positive, move up the scale to the top:
- 1 -- Easy to scratch with a fingernail, oily and soft to the touch (corresponds to a stearite cut)
- 2 -- Can be scratched with a fingernail (plaster)
- 3 -- Can be easily cut with a knife or nail, scratched with a coin (calcite, lime spar)
- 4 -- Easy to scratch with a knife (fluorspar)
- 5 -- Can hardly be scratched with a knife, can be scratched with a piece of glass (apatite)
- 6-- Can be scratched with a file, the file itself, with force, can scratch the glass (orthoclase)
- 7-- Can scratch steel for files, easily scratches glass (quartz)
- 8 -- Scratches quartz (topaz)
- 9 --Scratches almost anything, cuts glass (corundum)
- 10 -- Scratches or cuts almost anything (diamond)
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Break the mineral and study what pieces it breaks down into. Due to the fact that each mineral has a certain structure, it must break down into parts in a certain way. If you observe more flat surfaces in faults of the same rock, then we are dealing with cleavage. If there are no flat surfaces, but continuous chaotic bends and bulges are observed, then there is a fracture in the mineral.
- Cleavage is described in more detail using the number of planes obtained during the fault (usually from one to four); the concept is also taken into account perfect(smooth) or imperfect(rough) surface.
- There are several types of fractures. They are described as splinter-like ( fibrous), sharp and jagged ( hooked), cup-shaped ( shellish, snail-shaped) or none of the above ( uneven).
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If you still have not identified your mineral, you can conduct additional experiments. Geologists have many other tests at their disposal to classify minerals. However, many are simply not useful for identifying the most common species, and many will require special equipment or hazardous materials. Here is a brief description of several experiments that may be necessary:
If the mineral comes off in layers when rubbed, it is probably mica. This mineral is easy to identify, because if you scratch it with a fingernail or even just a finger, it separates into thin plates. Potassium” (or white) mica pale brown or colorless, whereas magnesia” (or black) mica is dark brown or black, with gray-brown veins.
Now let's understand the difference between gold and “cat” gold. Pyrite, also known as “cat” gold, also looks like a shiny yellow metal, but a couple of tests is enough for the difference to become obvious. Pyrite has a hardness rating of up to, and sometimes exceeds, 6; gold, on the other hand, is much softer, ranging between 2 and 3. It leaves a greenish-black streak and can crumble under sufficient pressure.
First, let's understand the difference between minerals and regular stones. A mineral is a natural combination of chemical elements that forms a specific structure. And, despite the fact that you can find the same mineral in different shapes and colors, it will still show the same properties when tested. In contrast, stones may be made up of a combination of minerals and do not have a crystal lattice. They are not always easy to distinguish, however, if the experiment produces different results from different sides of the object, then the object is most likely a stone.
To determine minerals, there are many methods that require special instruments and laboratories (chemical, crystallographic, X-ray analyses). At the same time, the simplest one is known - macroscopic a method for determining minerals based on the study of their external features: crystal morphology, simple mechanical properties (hardness, fracture, cleavage, etc.), optical (color, shine, transparency), etc.
When macroscopically determining minerals, the following rules must be followed:
determination of any characteristic is always carried out on the most recent split surface;
the sample must be moved slightly so that the light falls on it from different angles;
always compare the characteristics of the sample under study with the corresponding characteristics of already known samples;
adhere to the following definition sequence: hardness → shine → cleavage → fracture → color in the piece → line → other properties;
immediately after determining each characteristic, you should write it down in a notebook;
always first determine all the specified properties, and only then begin searching for the corresponding sample in the literature (mineral identification).
Hardness is the most important property in determining minerals. The hardness of a mineral is its ability to withstand external mechanical stress. The hardness of minerals depends on the characteristics of their internal structure, as well as on their chemical composition. For example, graphite and diamond, although composed of the same element (carbon), have completely different hardness because their crystal lattices are not the same. On the other hand, limonite samples can also vary dramatically in hardness due to different contents of water molecules - the more water molecules, the lower the hardness. In this regard, it is important to remember that, firstly, hydrated compounds are always softer than anhydrous ones (like bauxite and corundum), and secondly, that there are a significant number of minerals whose hardness varies. The simplest way to determine hardness is to scratch one mineral with another. To assess relative hardness, the Mohs scale is adopted, represented by ten standard minerals, the hardness of which is constant. On the Mohs scale, each subsequent mineral scratches all previous ones (the higher the number of the mineral, the harder it is).
Talc – 1.
Calcite – 3.
Fluorite – 4.
Apatite – 5.
Orthoclase – 6.
Quartz – 7.
Topaz – 8.
Corundum – 9.
Diamond – 10.
There are no known minerals in nature that are between corundum and diamond in hardness. Therefore, diamond is not required for practical determination of hardness. To determine the hardness of the mineral under study, select a smooth area on its surface and, pressing strongly, draw an acute angle of the mineral from the Mohs scale along it. If a scratch remains on the mineral under study, then its hardness will be lower than that of the mineral on the Mohs scale; if there is no scratch, then the hardness of the mineral under study is greater than the reference one. The test is carried out until the mineral being tested falls within the range between two minerals on the hardness scale, i.e. its hardness will not be determined as intermediate between them or as equal to one of them. Some common objects are often used to determine hardness. Thus, the hardness of a soft pencil is I; nails – 2; glass 5–5.5; steel needle and steel knife 6–7.
Shine of a mineral depends on its ability to refract and reflect rays and on the nature of the reflecting surface itself. There are minerals with a metallic and non-metallic luster. Metallic luster is characteristic of minerals that reflect light like steel. Many sulfides, iron oxides, and native metals have this luster. Shine semi-metallic(metallic) somewhat duller, it is characteristic of graphite. Glass luster is characteristic of the cleavage planes of many transparent or translucent minerals (calcite, gypsum, feldspars, faces of quartz crystals). Fatty luster (fracture of quartz, nepheline) resembles the luster that appears on a surface lubricated with oil. Pearl luster is inherent in minerals, the surface of which shines like the inner (pearl) surface of a shell (mica, talc). Silky the shine resembles the shine of silk fabric and is characteristic of minerals with a fibrous structure (selenite, asbestos). Wax Some cryptocrystalline and amorphous aggregates (flint) have a luster similar to the luster of the surface of a candle. Matte gloss essentially means the absence of shine - in this case, the surface reflects light evenly dimly, like writing chalk. A matte sheen is characteristic of earthy varieties with a finely porous surface (kaolin, bauxite). Simultaneously with the identification of shine, it is convenient to determine the cleavage and fracture of the mineral.
Cleavage – the ability of minerals to split along planes. The cleavage planes coincide with those planes of the crystal lattice in which the adhesive forces between atoms are minimal. To detect cleavage, the mineral should be turned toward the light so that some part of its surface reflects light into the eyes. If the sample under study has cleavage, then on the shiny surface you can see many light-reflecting plates, layered on top of each other, and forming a kind of staircase. All these shiny plates (cleavage planes) lie parallel, and are separated by the thinnest dark lines. In many minerals, cleavage is expressed in several directions, intersecting each other. For example, in micas (muscovite, biotite), cleavage can be traced only in one direction. In halite and sylvite - in three directions, perpendicular to each other (cleavage along the cube). Sphalerite has six directions of cleavage planes. There are several types of cleavage: very perfect, perfect, average and imperfect. Very perfect Cleavage is manifested in the fact that the mineral is very easily (with a fingernail, a knife blade) split in a certain direction into thin parallel plates with a smooth shiny surface (mica, talc, chlorite). Perfect cleavage is expressed in the fact that the mineral, when lightly struck with a hammer, splits along even parallel planes (calcite, feldspar). Average Cleavage is detected with a strong impact; the planes of cleavage can be distinguished with some difficulty. Imperfect Cleavage is difficult to detect (apatite, beryl). These are practically minerals without cleavage. Without sufficient skill, cleavage planes can sometimes be confused with crystal faces. Please keep the following in mind:
on cleavage planes, minerals usually shine more than on the edges of crystals and any other fracture surfaces;
In the cleavage plane of the mineral, you should always find several plates parallel to each other, successively layered on top of each other (like steps).
Simultaneously with the determination of cleavage (and shine), it is possible to identify the fracture of the mineral.
Kink . When splitting various minerals, you will notice that the resulting surface is different. Depending on the nature of this surface, fractures are of the following types:
granular - the surface is formed by many fused grains and spheres; characteristic of oolitic aggregates;
earthy – characterized by a rough matte surface (kaolinite);
conchoidal – has the appearance of a concave, concentrically wavy surface (flint);
splintered - the surface is formed by equally oriented needles (hornblende);
stepped - a surface in the form of steps separating cleavage planes (feldspars, halite, galena);
uneven - a chaotically broken shiny surface of solid minerals lacking cleavage (nepheline).
Color minerals is an important diagnostic feature. Minerals have different colors: white, gray, yellow, red, green, blue, black. They may also be colorless. In practice, the color of minerals is determined by eye by comparison with familiar objects: milky white, apple green, straw yellow, etc. The color of minerals depends on their chemical composition and impurities. Some minerals (labradorite) change color depending on lighting conditions, acquiring a beautiful rainbow color. This property of minerals is called iridization . Sometimes, in addition to the main color, the thin surface layer of the mineral has an additional color, and its surface shimmers in blue, red, pinkish-violet (chalcopyrite, bornite). This phenomenon is called tarnish . Tarnishing is explained by the interference of light in thin films formed on the surface of the mineral as a result of various reactions. There is also a significant number of minerals that do not have a constant color (quartz, halite, nepheline, etc.), and, accordingly, color cannot be a diagnostic feature for them. In such cases, as well as when other external features of different minerals coincide, determining the feature turns out to be useful.
Trait is the color of the mineral powder. Many minerals have a different color when crushed or powdered than in the lump. So, pyrite in a piece is straw-yellow in color, but in powder it is almost black. To determine the trait, a piece of mineral is passed several times on an unglazed porcelain plate (provided that the hardness of the mineral is less than the hardness of porcelain). If the mineral is too hard, the powder is obtained by grinding it with an even harder mineral. As a rule, if it is not possible to determine the color of the powder using porcelain, then they write that the mineral does not have a feature.
Others properties combine other, often strictly individual, characteristics of minerals. However, other properties often play a critical role in diagnosis, especially for related minerals (halite and sylvite). Specific weight depends on the chemical composition and structure of the mineral. All minerals can be divided by specific gravity into three groups: lungs with a specific gravity of less than 2.5 (amber, gypsum, halite); medium - with a specific gravity of 2.5-5 (apatite, corundum, sphalerite); heavy - with a specific gravity greater than 5 (cinnabar, galena, gold). The specific gravity of minerals in the field is determined approximately by weighing it on the hand (only one mineral should be present in the sample). Transparency – release minerals opaque, i.e. do not transmit light rays even in very thin plates (native metals, many sulfides, iron oxides); translucent only in a thin plate (on a thin edge, like feldspars, flint, many carbonates); translucent, transmitting light like frosted glass (gypsum, chalcedony); transparent, transmitting light like ordinary glass (rock crystal, Iceland spar). Some minerals have special, unique properties. For example, the ability of carbonate minerals to enter into reaction with hydrochloric acid ("boil"). A number of minerals are characterized magnetism (magnetite, pyrrhotite) - they deflect the magnetic needle. For diagnostics in field conditions it is important solubility minerals in water or acids and alkalis. Halite and sylvite are easily soluble in water. These same minerals have taste – salty in halite, bitterly salty in sylvin. Natural alum has a sour, astringent taste. Sometimes minerals have smell . Thus, arsenopyrite and native arsenic smell like garlic when struck; pyrite, marcasite – emit the smell of sulfur dioxide; Phosphorite when rubbed has the smell of burnt bone. Some minerals greasy to the touch (talc), others - easy get dirty hands (graphite, pyrolusite). Double refraction has Iceland spar. Fluorescence characteristic of fluorite. Hygroscopicity possess kaolin, sylvite, carnallite. Radioactivity minerals containing uranium and thorium are different.
To determine minerals, they use determinants and tables, which are compiled based on the study of their physical properties. Having determined the hardness, it is necessary to establish the luster of the mineral, then the color of the line, cleavage and other external signs. Next, taking into account the hardness and luster of the mineral, we find in the table a description that most closely matches all the physical properties of the sample being studied. Minerals in the table are arranged in order of increasing hardness (soft, medium hard, hard), each group takes into account luster (metallic, non-metallic).
Stone lovers are often faced with the need to identify a mineral that was accidentally found, purchased or given as a gift, the name of which they were not told. And I want to know him. It must be said right away that most minerals can only be accurately identified by a specialist geologist.
Geology and mineralogy are fields of knowledge bordering on craft. It is impossible to know mineralogy without holding rocks and minerals in your hands. We can say that such knowledge is passed on by word of mouth. Teachers, and later colleagues, who worked in deposits with specific minerals and participated in laboratory studies, know what kind of mineral they are being shown. And they will definitely say the name. You need to feel it with your hands, see it with your own eyes, perhaps even smell it and try the mineral on your tooth in order to remember it. And not just one sample, but many, so that you know all the varieties.
A specialist can say a lot about a stone - where it comes from, what its origin is, how and at what temperature it was formed, what minerals it is associated with in nature. Stone lovers, of course, also know the names of many minerals. But only after they were called by a specialist who was also taught by someone. From word of mouth...
If a cabochon or faceted insert is made from a mineral, the matter becomes even more complicated. Many jewelry stones in products are similar to each other in color and shine. But you cannot touch, scratch or drip acid onto such a stone. Here the geologist can shrug his shoulders, name several options and send you to a gemological laboratory, where there are many instruments that allow you to make a determination without damaging the insert.
How to identify a mineral, without being a narrow specialist, is it possible to do this? You can also try. Definition usually begins with color stone It seemed that nothing could be simpler: all people, with the exception of colorblind people, see colors approximately the same. But what to name the color? Each color can have dozens of shades.
What is the correct name for the color of malachite? Jade? Emerald? Red color: it is completely different between ruby and coral, yellow minerals have an innumerable number of shades. There are many funny descriptions in geologists' field notebooks. I have come across, for example, “salad-apple”, “meat-red” colors, “the color of a champagne bottle”, “the color of a red sunset” and even “the color of a male pigeon’s wing feather”... Conclusion: describe the color so that everyone can imagine it , very hard.
A mineral is a property of a stone that is much easier to determine. Exists Mohs relative hardness scale , in which the hardness of minerals is compared with the hardness of standard minerals and ordinary objects, of which there are many around.
Thus, a mineral is scratched or not scratched by glass, a copper coin, a knife, a fingernail, or a file. After such a test, the relative hardness is determined from the table. For example, it is often impossible to distinguish vein quartz from calcite by eye. But quartz has a hardness of 7 units (a steel knife leaves a mark on it), and calcite has a hardness of 3 units (it crumbles with a knife). Graphite is easily scratched with a fingernail. And so on. The scale was compiled by the naturalist Mohs more than 150 years ago. Since then, nothing has been changed in the scale, and why change something that works well?
Stroke color may not match the color of the crystal. Thus, black hematite with a metallic sheen leaves a cherry or brown streak on the ceramic briquette. Golden pyrite produces a black streak, unlike native gold, which has a golden yellow streak.
Shine mineral is one of the most difficult diagnostic signs. How to distinguish glass shine from diamond, oil from wax? This is difficult to do without experience and practice.
Appearance crystals are varied, but at first glance it is not always possible to accurately name the mineral. The problem is that a wide variety of crystals can have a similar appearance. For example, tourmaline, topaz, apatite, and beryl are similar in crystal shape. And there are many such examples.
After identifying all available positions, they begin to determine the mineral using special reference books. They are now available on the Internet and in print. These are usually good, carefully made guides, but, unfortunately, when using them, the error rate reaches 50 percent or more. Why? Because to identify a mineral, you need someone to show it to you, let you touch it, smell it and taste it...
There are scientific classifications of minerals that are used by specialists all over the world. When they get tired of serious work, they come up with such humorous classifications (see below).
Minerals differ in their specific chemical composition and external physical characteristics. These include: shine, hardness, color, fracture pattern. Identifying minerals by external signs is not difficult, but it requires attention and accuracy.
Determining the chemical composition of a mineral is a more difficult task. Our determinant provides formulas only for those minerals that have a simple chemical composition.
After reading this chapter, you will become familiar with techniques for identifying the most common minerals.
Colored tables for identification will help you find out the name of the mineral that fell into your hands.
When identifying minerals by appearance, you must first pay attention to the characteristics common to all minerals, and then consider the features that distinguish them from each other.
First of all, pay attention to the shine of the mineral.
Most minerals, due to the reflection of light rays by their surfaces, shine, and only some of them - matte - lack shine.
Based on their luster, minerals are easily divided into two groups: minerals with a metallic luster and minerals with a non-metallic luster.
MINERALS WITH METAL LUSTER 1 - radial-radiant crystals of stibnite - antimony luster - on barite; 2 - crystal of pyrite - sulfur pyrite; 3 - galena (dark) - lead luster - in quartz; 4 - galena crystal in barite; 5 - sinter hematite - the so-called “red glass head”; 6 - crystal of iron luster; 7 - a piece of solid hematite - red iron ore; 8 - magnetite crystals in chlorite slate.
Metallic shine:
1. The metallic luster resembles the luster of the surface of a freshly fractured metal. Metallic luster is better visible on a fresh (non-oxidized) metal surface. Minerals that have a metallic luster are opaque and heavier than minerals that have a non-metallic luster. Sometimes, due to oxidation processes, minerals that have a metallic luster become covered with a dull crust.
Metallic luster is characteristic of minerals that are ores of various metals. Examples of minerals that have a metallic luster include gold, copper pyrite, and lead luster.
2. Metallic luster - duller, like that of metals that have become tarnished by time. Example: magnetic iron ore.
Non-metallic luster:
1. Glass luster resembles the luster of glass surface. They are possessed by: rock salt, rock crystal.
2. Diamond shine - sparkling, reminiscent of glass, but stronger. Examples: diamond, zinc blende.
3. Mother-of-pearl luster is similar to the luster of mother-of-pearl (the surface of the mineral casts rainbow colors). Often observed, for example, in calcite and mica.
4. Silky shine - shimmering. Characteristic only for minerals that have a fibrous or needle-like structure. Example: asbestos.
5. Oily sheen has the peculiarity that the surface of the mineral seems to be greased. Sometimes the mineral itself is greasy to the touch, such as talc.
6. Waxy sheen is similar to oily sheen, but weaker. Example: chalcedony.
Matte minerals lack shine and resemble earthy masses. Example: bauxite.
The shine is best observed on a fresh fracture of a mineral or on the fresh surface of the faces of its crystals. After you have established the nature of the shine, you need to determine the hardness of the mineral.
Mineral hardness
The hardness of a mineral is the resistance it offers when you scratch it with some other object or mineral. If the mineral being tested is softer than the one with which you scratch on its surface, then a mark will remain on it - a scratch.
Scientists have compiled the following scale of mineral hardness:
The vast majority of minerals common in the earth's crust have a hardness of no more than 7. Only a small number have a greater hardness.
The hardness of minerals can be determined using a fingernail and a piece of ordinary glass.
Based on hardness, all minerals are divided into three groups:
1. Soft minerals (the fingernail leaves a scratch on the mineral). Examples: talc, graphite, gypsum.
2. Minerals of medium hardness (a fingernail does not leave a scratch on a mineral; a mineral does not leave a scratch on glass). Examples: crystalline calcite, copper pyrite, or chalcopyrite.
3. Hard minerals (the mineral leaves a scratch on the glass). Examples: quartz, feldspars.
After the test, it is necessary to wipe off the powder, i.e., crushed particles of the mineral, from its surface and make sure that a trace actually remains on the mineral, since the powder could have formed from the mineral that was used to scratch.
The color of the streak (or, in other words, the color of the powder) of some minerals does not differ from the color of the mineral itself; but there are also minerals whose powder color differs sharply from their color. For example, calcite is colorless, white, yellow, green, blue, indigo, violet, brown, black; Calcite powder is always white.
To obtain mineral powder (i.e. trait), a rough, unglazed porcelain plate is used - the so-called biscuit. You can replace the biscuit with a shard of unglazed porcelain or a fragment of earthenware, after first removing the smooth layer of glaze from it with sandpaper or a file.
If you run a mineral along the surface of a biscuit or along a rough fracture of a porcelain shard, the mineral will leave a line.
All soft and medium-hard minerals, with a few exceptions, give a trait; Most solid minerals do not produce the trait.
If you don’t have a porcelain plate at hand, you can scrape the mineral with a knife to get a fine powder. To determine the color of a line, this powder should be ground on white paper.
Color appears to be a constant feature for few minerals. So, for example, malachite is always green, gold is golden yellow, etc. For most minerals this sign is not constant. To determine the color of a mineral, it is necessary to obtain a fresh fracture.
Fractures of minerals can also be different. So, for example, flint is distinguished by a conchoidal fracture, lead luster has a step fracture, many minerals have earthy, splinter and other fractures.
The type of fracture depends on the physical properties of the mineral, its crystal structure and hardness.
Some minerals are characterized by cleavage, that is, the ability to split or split in certain directions. In this case, smooth, shiny cleavage planes are formed. For example, micas are characterized by pronounced cleavage. They can easily separate into thin, smooth leaves in one direction. Rock salt is distinguished by well-defined cleavage in three directions: if you split a fragment of a rock salt crystal, all the fragments will have the correct cube shape.
Specific gravity is not an important characteristic for most minerals, but for minerals that contain heavy elements such as lead, specific gravity is of great importance in the determination.
Classification of minerals by external characteristics does not require determination of specific gravity with great accuracy. It is enough to divide minerals into two main groups: light and heavy.
For some minerals, the distinguishing feature is magnetism. Minerals containing iron are sometimes magnetic, such as lodestone. Magnetism in other iron-containing minerals appears after calcination.
To determine the magnetism of minerals, a magnetic needle suspended on a thin point is used, and in the field, a compass needle is used. Minerals that have magnetic properties, when brought close to a magnetic needle, attract it towards themselves.
Some minerals containing carbon dioxide, under the influence of hydrochloric acid (10% solution), release carbon dioxide in the form of bubbles - as they say, the mineral “boils”. These include: calcite, malachite and rocks - chalk, limestone.
There are minerals that can be recognized by taste, for example, rock salt, potassium salts (sylvite, carnallite), etc.
When starting to identify an unknown mineral, use first of all the first part of our determinant, i.e. “”.
Using the key, first of all you must determine what kind of luster your mineral has - metallic or non-metallic. Having established this, you successively determine the hardness of the mineral, the color of the line, etc. The data obtained about the mineral will ultimately lead you to certain pages of the second part of the determinant, where various minerals are described. The "Key to the Mineral Guide" lists these pages.
If it becomes necessary to examine a mineral for combustion or fusibility, you should break off a small piece from it, hold it with the tips of tweezers and insert it into the flame of a candle, alcohol lamp or gas burner. Some minerals, such as amber, ignite even in the flame of a match.