Methods for determining minerals. How to identify minerals

There are so many minerals - perhaps part of the reason 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 that can be compared with the results of the experiments. You can even go to the description 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 will learn how to tell real gold from other shiny yellow minerals, read about streaks of brilliant colored layers in the rock, or learn how to determine what kind of strange mineral that flakes into plates when rubbed.

Steps

Part 1

Conducting experiments

First, let's understand the difference between minerals and ordinary stones. A mineral is a natural combination of chemical elements that forms a certain 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 can be composed of a combination of minerals and do not have a crystal lattice. It is not always easy to distinguish them, however, if the experiment gives different results from different sides of the object, then the object is most likely a stone.

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.

Learn to navigate the classification of minerals. Thousands of minerals have found a place on our planet, but many of them are 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 does not fit any of the above descriptions, try consulting your region's mineral classifier. If you have done a lot of experiments, but have not been able to reduce the number of options to two or three, look on the Internet. Look at the photos of each mineral that looks like yours and look for all the possible tips on how to distinguish these minerals.
- It is better to include at least one test that requires exposure to the mineral, such as a hardness test or a stroke test. Experiences that involve only viewing and describing may turn out to be biased, since different people describe the same minerals in different ways.
Study the shape and surface of the mineral. The set of forms of each mineral and the characteristic features of a group of minerals is called the "general form". To describe these characteristics, geologists have a variety of technical terms, but usually a general description is enough. For example, is your mineral bumpy, rough, or smooth? What is it: a mixture of rectangular crystals, or is your specimen bristling with sharp crystal peaks?

Take a closer look at how your mineral shines. Luster refers to the way a mineral reflects light, and although this is not a scientific test, it may be useful to describe. Most minerals have a "glassy" ("glossy") or metallic sheen. However, you can also describe gloss as "thick", "pearl" (whitish sheen), "matte" (dull, like unglazed ceramic), or any other definition you feel is accurate. .

Pay attention to the color of the mineral. Most people do not see any difficulty in this, but, meanwhile, this experience may be useless. Small foreign inclusions can cause a change in color, which is why you can find the same mineral in different colors. However, if the mineral has an unusual color, say purple, this can narrow your search considerably.
- When describing minerals, avoid fancy color names like "salmon" or "puce". Try to get by with just red, black and green.
Experiment with a stroke. This is a useful and easy test, as long as you have a piece of white unglazed porcelain. The reverse side of the tiles from the bathroom or kitchen is perfect; maybe you can buy something suitable at the repair supply store. Having become the owner of the coveted piece of porcelain, just rub the mineral on the tile and see what color stroke it leaves. Often the color of the stroke will differ from the base color of the mineral.
- Glaze gives porcelain and other types of ceramics a glassy (glossy) sheen.
- Be aware that some minerals do not leave a streak, especially hard minerals (as they are harder than a streak plate).
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 factor "4", but does not reach "5", then the coefficient of your mineral is between "4" and "5", you can stop the experiment. Try scratching your mineral using the common items listed 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 fingernail, feel oily and soft (corresponds to stearite notch)
- 2 -- Can be scratched with a fingernail (gypsum)
- 3 -- Can be easily cut with a knife or nail, scratched with a coin (calcite, calcareous)
- 4 -- Easy to scratch with a knife (fluorspar)
- 5 -- Difficult to scratch with a knife, can be scratched with a piece of glass (apatite)
- 6-- Can be scratched with a file, he, with effort, can scratch glass (orthoclase)
- 7-- Can scratch file steel, easily scratches glass (quartz)
- 8 -- Scratches quartz (topaz)
- 9 -- Scratches almost anything, cuts glass (corundum)
- 10 -- Scratches or cuts almost anything (diamond)
Break the mineral and study what pieces it breaks into. Due to the fact that each mineral has a certain structure, then it must break up into parts in a certain way. If you observe more flat surfaces in faults of the same rock, then we are dealing with cleave. If there are no flat surfaces, but continuous chaotic bends and bulges are observed, then a fracture is present in the mineral.
- The cleavage is described in more detail by the number of planes produced by the fracture (usually one to four); also takes into account the concept perfect(smooth) or imperfect(rough) surface.
- Breaks are of several types. They are described as splintery ( fibrous), sharp and serrated ( hooked), bowl-shaped ( shelly, cochlear) or none of the above ( uneven).
If you still have not identified your mineral, you can conduct additional experiments. There are many other tests available to geologists for classifying minerals. However, many are simply not useful for identifying the most common species, many requiring special equipment or hazardous materials. Here is a summary of a few experiences that may be necessary:

If the mineral comes off in layers during friction, it is probably mica. This mineral is easy to identify, because if you scratch it with a fingernail or even just a finger, it delaminates into thin plates. Potassium” (or white) mica pale brown or colorless, while magnesian” (or black) mica is dark brown or black, with gray-brown streaks.

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 experiments are enough to make the difference obvious. Pyrite has a hardness factor of up to and sometimes exceeds 6, while gold is much softer, ranging between 2 and 3. It leaves a greenish-black streak and can crumble under sufficient pressure.

Determination of minerals, simple diagnostic methods without instruments

The described evaluation methods do not always allow for an accurate determination of the mineral. Reliable determination requires quantitative chemical analysis and X-ray crystallography, and this requires a specialized laboratory. Hobbyists and collectors are always able to succeed in practical determinations, using visual, physical, optical and morphological qualities and applying some elementary chemical methods.

We will have to confine ourselves to simple methods, making determinations by the method of successive elimination and not using the complex tools of a professional.

To begin with, we take a fairly fresh sample of the mineral and, if necessary, separating it from a larger piece. We examine it as closely as possible, first with the naked eye, and then with a magnifying glass, noting any recognizable properties. It is necessary to accurately record all established observations - in this case we will succeed even if the result is not clear enough and we have to repeat the definition of some properties. We focus our attention on the external form and appearance of the mineral, its state of aggregation (if it is polycrystalline), on the presence of twins, on symmetry elements. Then follows the study of the color of the mineral, checking the color of the line, since the mineral may appear uncolored purely externally.

Indications of brilliance in many cases can be questionable, so possible alternatives should be noted in the records. The same applies to transparency.

We determine the hardness using the simplified methods described above, and only then we check it with greater accuracy and identify it on the hardness scale. Then we reduce the gap between the hardness values and check it within the limits available to us according to the diagnostic map.

Our further observations relate to the presence of cleavage in the mineral and (if it is found) to the study of the nature of the cleavage surface.

Then we check the fragility, the size of the fragments, flexibility and elasticity. Weighing on the hand, we estimate the specific gravity. We expose a piece of the mineral to the action of water and a solution of hydrochloric acid. Finally, we note the accompanying minerals (paragenesis), which in many cases facilitates identification.

Well-formed crystals are found within the rock mass. Phosgenite on the left. Right: green annabergite crystals formed in a geode

Left: well-formed garnet crystals embedded in rock mass. Right: schorl black tourmaline and orthoclase

SOME EXAMPLES OF DETERMINATION OF MINERALS

It is likely that at the end of all our actions there may be doubts about the correctness of the diagnosis. How to get out of them? Let's try to show the output with a few examples.

Aggregates of granular magnetite are very similar to the same formations of chromite. But the color of the line in magnetite is black, and in chromite it is brown. In addition, magnetite has a magnetic effect on the compass needle, while chromite does not.

When the outlines of the crystals are not too clear, dense pyrite with an iridescent tint is difficult to distinguish from chalcopyrite. They have the same line color. But then it can be established that pyrite is harder (6) than chalcopyrite (4.5).

Black sphalerite and black cassiterite have the same semi-metallic luster. But they can be distinguished by hardness. For sphalerite it is 3.3, for cassiterite it is 6.5. In addition, sphalerite often occurs together with other sulfides, and quartz and mica are present in association with cassiterite.

Fluorite, amethyst and apatite differ in the shape of the crystal. But their granular aggregates can have an almost identical purple color, and the shape in this case is difficult to distinguish. Amethyst among these minerals is the hardest - it is not scratched by the blade of a penknife and, moreover, does not have cleavage. Fluorite has perfect cleavage and is recognized by its luminescence during heating. Apatite is harder than fluorite and has imperfect cleavage.

Augite, hornblende and tourmaline often form more or less elongated prisms that are very similar. Tourmaline is recognized by the absence of cleavage and the presence of typical banding on the prism faces. In addition, it is more common in acidic rocks.

In contrast, augite and hornblende form in the base rocks. They differ in the nature of cleavage. Augite has two good cleavages almost at right angles, while hornblende has perfect cleavage at 125o.

Feldspars, calcite, barite, and gypsum are often whitish in color and are similar in their perfect cleavage. Gypsum is easily excluded, as it is scratched by a fingernail, and feldspars, which are scratched by a knife. Barite and calcite have the same hardness, but they can be distinguished as barite is much harder. In addition, under the influence of a solution of hydrochloric acid, calcite boils with a hiss.

Topaz is 2 times heavier than a similar piece of quartz.

For the determination of minerals, there are many methods that require special instruments and laboratories (chemical, crystallographic, X-ray analysis). However, the simplest is known - macroscopic a method for determining minerals based on the study of their external features: crystal morphology, the simplest properties of mechanical (hardness, fracture, cleavage, etc.), optical (color, luster, transparency), etc.

When macroscopically determining minerals, the following rules must be followed:

the determination of any characteristic is always carried out on the most recent split surface;

the sample must be slightly moved so that the light falls on it at different angles;

always compare the characteristics of the test sample with the corresponding characteristics of already known samples;

adhere to the following definition sequence: hardness → gloss → cleavage → fracture → color in a piece → line → other properties;

immediately after determining each characteristic, write it down in a notebook;

always first determine all the indicated properties, and only then start searching for the corresponding sample in the literature (determinant of minerals).

Hardness is the most important property in the determination of minerals. The hardness of a mineral is its ability to withstand external mechanical stress. The hardness of minerals depends on the features of their internal structure, as well as on the chemical composition. For example, graphite and diamond, although they consist of the same element (carbon), have completely different hardnesses, since their crystal lattices are not the same. On the other hand, limonite samples can also differ dramatically in hardness due to the different content 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 is variable. The easiest way to determine hardness is to scratch one mineral with another. To assess the relative hardness, the Mohs scale was adopted, represented by ten reference minerals, the hardness of which is constant. In the Mohs scale, each subsequent mineral scratches all the 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.

In nature, no minerals are known 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, a smooth area is selected on its surface and, pressing strongly, a sharp corner of the mineral from the Mohs scale is drawn along it. If a scratch remains on the mineral under study, then its hardness will be less than that of the Mohs scale mineral; if there is no scratch, then the hardness of the studied mineral is greater than the reference. The test is carried out until the tested mineral is in the interval between two minerals from the hardness scale, i.e. its hardness will not be defined as intermediate between them or as equal to one of them. To determine the hardness, some common objects are often used. So, the hardness of a soft pencil is I; nails - 2; glasses 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 reflective surface itself. There are minerals with metallic and non-metallic luster. Metallic luster is inherent in minerals that reflect light like steel. Many sulfides, iron oxides, and native metals have this brilliance. Shine semi-metallic(metallic) somewhat dimmer, it is characteristic of graphite. Glass gloss is characteristic of the cleavage planes of many transparent or translucent minerals (calcite, gypsum, feldspars, quartz crystal faces). Fatty brilliance (quartz fracture, nepheline) resembles the brilliance that appears on a surface lubricated with oil. Pearl brilliance is inherent in minerals, the surface of which glistens like the inner (mother-of-pearl) surface of the shell (mica, talc). Silky shine resembles the shine of silk fabric, characteristic of minerals with a fibrous structure (selenite, asbestos). Wax some cryptocrystalline and amorphous aggregates (flint) have a luster similar to that of a candle surface. Matte luster essentially means the absence of luster - while the surface reflects light evenly dimly, like writing chalk. A matte sheen is inherent in earthy varieties with a finely porous surface (kaolin, bauxite). Simultaneously with the detection of gloss, 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 adhesion forces between atoms are minimal. To detect cleavage, the mineral should be turned towards the light so that some part of its surface reflects the light into the eyes. If cleavage is present in the sample under study, then on a shiny surface one can see a lot of 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, mutually intersecting. For example, micas (muscovite, biotite) have cleavage in only one direction. Halite and sylvin have three directions perpendicular to each other (cube cleavage). Sphalerite has six directions of cleavage planes. There are several types of cleavage: very perfect, perfect, medium 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 hit with a hammer, splits along even parallel planes (calcite, feldspar). Medium cleavage is detected with a strong impact, while the cleavage planes may differ with some difficulty. imperfect cleavage is found with difficulty (apatite, beryl). These are practically minerals without cleavage. In the absence of sufficient skill, cleavage planes can sometimes be confused with crystal faces. Keep in mind the following:

on cleavage planes, minerals usually shine more strongly than on crystal faces and any other fracture surfaces;

in the cleavage plane of the mineral, one should always find several plates parallel to each other, sequentially layered on top of each other (such as steps).

Simultaneously with the determination of cleavage (and gloss), it is possible to identify a fracture of the mineral.

kink . When splitting various minerals, one can 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 intergrown grains, spheres; characteristic of oolitic aggregates;

earthy - characterized by a rough matte surface (kaolinite);

conchoidal - has the appearance of a concave, concentrically wavy surface (flint);

splintery - the surface is formed by equally oriented needles (hornblende);

stepped - a surface in the form of steps separating the cleavage planes (feldspars, halite, galena);

uneven - randomly fractured shiny surface of solid minerals, devoid of cleavage (nepheline).

Color minerals is an important diagnostic feature. Minerals have a different color: 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 well-known objects: milky white, apple green, straw yellow, and so on. The color of minerals depends on their chemical composition and impurities. Some minerals (Labrador) change color depending on the lighting conditions, acquiring a beautiful iridescent color. This property of minerals is called iridescence . Sometimes, in addition to the main color, a thin surface layer of the mineral has an additional color, while its surface shimmers in blue, red, pinkish-violet (chalcopyrite, bornite). This phenomenon is called discoloration . The tint 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 amount of minerals that do not have a permanent 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 various minerals coincide, it turns out to be useful to determine the feature.

trait is the color of the mineral powder. Many minerals in a crushed or powdered state have a different color than in a piece. So, pyrite in a piece is straw-yellow in color, and in powder it is almost black. To determine the trait, a piece of the mineral is passed several times over an unglazed porcelain plate (provided that the hardness of the mineral is less than the hardness of porcelain). If the mineral is too hard, then a powder is obtained by grinding it with an even harder mineral. As a rule, if using porcelain it is not possible to determine the color of the powder, then they write that the mineral does not have a feature.

Other properties combine other, often strictly individual features of minerals. However, other properties often play a critical role in diagnosis, especially in related minerals (halite and sylvine). 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 of more than 5 (cinnabar, galena, gold). The specific gravity of minerals in the field is determined approximately - by weighing on the hand (only one mineral should be present in the sample). Transparency - release minerals opaque, i.e. not transmitting light rays even in very thin plates (native metals, many sulfides, iron oxides); translucent only in a thin plate (along a thin edge, like feldspars, flint, many carbonates); translucent that transmit light like frosted glass (gypsum, chalcedony); transparent, transmitting light like ordinary glass (rock crystal, Icelandic spar). Some minerals have special properties that are unique to them. For example, the ability of carbonate minerals to enter into reaction with hydrochloric acid ("to boil"). A number of minerals are characterized magnetism (magnetite, pyrrhotite) - they deflect the magnetic needle. Important for field diagnostics solubility minerals in water or acids and alkalis. Halite and sylvin are readily soluble in water. These same minerals have taste - salty in halite, bitter-salty in sylvin. Natural alum has a sour, astringent taste. Sometimes minerals are smell . So, arsenopyrite and native arsenic smell like garlic when struck; pyrite, marcasite - emit the smell of sulfur dioxide; phosphorite when rubbed - the smell of burnt bone. Some minerals greasy to the touch (talc), others - light get dirty hands (graphite, pyrolusite). Double refraction has Icelandic spar. Fluorescence characteristic of fluorite. hygroscopicity possess kaolin, sylvin, carnallite. radioactivity differ minerals containing uranium, thorium.

To determine minerals, determinants and tables are used, which are compiled on the basis of a 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. Further, taking into account the hardness and brilliance of the mineral, we find in the table the description that most of all corresponds to all the physical properties of the sample under study. Minerals in the table are arranged in order of increasing hardness (soft, medium hard, hard), in each of the groups, luster (metallic, non-metallic) is taken into account.

Minerals differ in a certain chemical composition and external physical features. These include: gloss, hardness, color, fracture character. Determining 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 contains formulas of only those minerals that have a simple chemical composition.

After reading this chapter, you will learn how to identify the most common minerals.

Color tables for identification will help you find out the name of the mineral that fell into your hands.

When determining minerals by appearance, you must first pay attention to the features common to all minerals, and then consider the features that distinguish them from each other.

First of all, pay attention to the brilliance of the mineral.

Most minerals, due to the reflection of light rays on their surfaces, shine, and only a few of them - matte - are devoid of shine.

According to their luster, minerals are easily divided into two groups: minerals with a metallic luster and minerals with a non-metallic luster.

MINERALS WITH METALLIC SHINE 1 - radial-radiant crystals of antimonite - antimony luster - on barite; 2 - a crystal of pyrite - sulfur pyrites; 3 - galena (dark) - lead shine - in quartz; 4 - galena crystal in barite; 5 - sintered hematite - the so-called "red glass head"; 6 - crystal of iron sheen; 7 - a piece of solid hematite - red iron ore; 8 - magnetite crystals in chlorite schist.

Shine metallic:

1. Metallic luster resembles the luster of the surface of a fresh fracture of metals. Metallic luster is best seen 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 sheen become covered with a matte crust.

Metallic luster is characteristic of minerals that are ores of various metals. Examples of minerals that have a metallic luster are gold, copper pyrite, and lead luster.

2. Metallic luster - duller, like metals that have faded from time to time. Example: magnetic iron ore.

Luster non-metallic:

1. Glass luster resembles the luster of a 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 iridescent colors). Often observed, for example, in calcite, mica.

4. Silky shine - shimmery. Characteristic only for minerals that have a fibrous or needle structure. Example: asbestos.

5. Oily sheen has the peculiarity that the surface of the mineral seems to be smeared with grease. Sometimes the mineral itself is greasy to the touch, such as talc.

6. Waxy sheen is similar to oily, but weaker. Example: chalcedony.

Matte minerals are devoid of luster and resemble earthy masses. Example: bauxite.

Shine is best observed on a fresh fracture of the mineral or on the fresh surface of the faces of its crystals. After you have established the nature of the luster, it is necessary 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 you scratch on its surface, then a mark will remain on it - a scratch.

Scientists have compiled the following scale of hardness of minerals:

The vast majority of minerals common in the earth's crust have a hardness not exceeding 7. Only a small amount has a greater hardness.

You can recognize the hardness of minerals with a fingernail and a piece of ordinary glass.

By hardness, all minerals are divided into three groups:

1. Soft minerals (the nail leaves a scratch on the mineral). Examples: talc, graphite, gypsum.

2. Minerals of medium hardness (the nail does not scratch the mineral; the mineral does not scratch the 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., the crushed particles of the mineral, from its surface and make sure that there really is a trace on the mineral, since the powder could form from the mineral that was scratched.

The color of the line (or, in other words, the color of the powder) in some minerals does not differ from the color of the mineral itself; but there are also such minerals, the color of the powder of which differs sharply from their color. For example, calcite is colorless, white, yellow, green, blue, indigo, violet, brown, black; the powder of calcite is always white.

To obtain a mineral powder (i.e., traits), 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 removing a smooth layer of glaze from it with sandpaper or a file.

If you draw 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 give traits.

If there is no porcelain plate at hand, you can scrape the mineral with a knife to get a fine powder. To determine the color of the line, this powder should be ground on white paper.

Color turns out to be a constant feature for few minerals. So, for example, malachite is always green, gold is golden yellow, etc. For most minerals, this feature is unstable. To determine the color of the mineral, it is necessary to obtain a fresh fracture.

Mineral fractures can also be different. So, for example, flint is distinguished by a conchoidal fracture, lead luster - by a stepped fracture, many minerals have earthy, splintery 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 split planes are formed. For example, micas are characterized by pronounced cleavage. They can easily separate into thin smooth leaves in one direction. Well-defined cleavage in three directions is distinguished by rock salt: if you split a fragment of a rock salt crystal, then all the fragments will have the correct shape of a cube.

Specific gravity is not an important feature for most minerals, but for minerals that contain heavy elements such as lead, specific gravity is of great importance in the determination.

The classification of minerals by external features does not require the 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 magnetic iron ore. The magnetism of other minerals containing iron appears after calcination.

To determine the magnetism of minerals, a magnetic needle suspended on a thin tip is used, and in the field, a compass needle is used. Minerals that have magnetic properties, when brought to a magnetic needle, attract it to themselves.

Some minerals that have carbon dioxide in their composition, under the action of hydrochloric acid (10% solution), emit 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 tasted, such as rock salt, potassium salts (sylvin, carnallite), etc.

When starting to identify an unknown mineral, first of all use the first part of our determinant, i.e. "".

According to the key, the first thing you need to determine is 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 obtained data on the mineral will lead you eventually to certain pages of the second part of the guide, where various minerals are described. In the "Key to the determinant of minerals" these pages are indicated.

If it becomes necessary to examine the mineral for combustion or fusibility, you should chip off a small piece from it, hold it with the tips of tweezers and put it into the flame of a candle, spirit lamp or gas burner. Some minerals, such as amber, ignite even in the flame of a match.

When macroscopically determining minerals, the following rules must be followed:

the determination of any characteristic is always carried out on the most recent split surface;

the sample must be slightly moved so that the light falls on it at different angles;

always compare the characteristics of the test sample with the corresponding characteristics of already known samples;

adhere to the following definition sequence: hardness → gloss → cleavage → fracture → color in a piece → line → other properties;

immediately after determining each characteristic, write it down in a notebook;

always first determine all the indicated properties, and only then start searching for the corresponding sample in the literature (determinant of minerals).

Talc - 1.

Calcite - 3.

Fluorite - 4.

Apatite - 5.

Orthoclase - 6.

Quartz - 7.

Topaz - 8.

Corundum - 9.

Diamond - 10.

Shine of a mineral depends on its ability to refract and reflect rays and on the nature of the reflective surface itself. There are minerals with metallic and non-metallic luster. Metallic luster is inherent in minerals that reflect light like steel. Many sulfides, iron oxides, and native metals have this brilliance. Shine semi-metallic(metallic) somewhat dimmer, it is characteristic of graphite. Glass luster is characteristic of the cleavage planes of many transparent minerals (calcite, gypsum, feldspars, quartz crystal faces). Fatty shine (a fracture of quartz, nepheline) resembles the shine that appears on a surface lubricated with oil. Pearl brilliance is inherent in minerals, the surface of which glistens like the inner (mother-of-pearl) surface of the shell (mica, talc). Silky shine resembles the shine of silk fabric, characteristic of minerals with a fibrous structure (selenite, asbestos). Wax some cryptocrystalline and amorphous aggregates (chalcedony, flint) have a luster similar to that of a candle surface. Matte luster essentially means the absence of luster - while the surface reflects light evenly dimly, like writing chalk. A matte sheen is inherent in earthy varieties with a finely porous surface (kaolin, bauxite). Simultaneously with the detection of gloss, it is convenient to determine the cleavage and fracture of the mineral.