Identification of mineral process performance - identification by reflective microscopy

The equiaxed crystal minerals belonging to the higher crystal family have only one reflectance value, and the mineral reflectance of other crystal systems varies with the crystal direction. When the stage is rotated, the change of the mineral brightness is observed. The phenomenon of change is called the double reflection of minerals. The tetragonal, trigonal, and hexagonal minerals belonging to the intermediate crystal family have two main reflectances, Ro and Re, and belong to the lower tritic, triclinic, monoclinic, and orthorhombic minerals. There are 3 main reflectivities Rg, Rm and Rp
(II) Determination of reflectivity and double reflection There are many methods for determining the reflectivity of minerals. In summary, they can be divided into two major categories: optical method and photoelectric method. The former is the most widely used by visual comparison method, and the latter is multiplied by photoelectric. The law is the most effective.
1. Visual comparison method The visual comparison method is a method of observing the brightness of an unknown mineral with a naked eye under a microscope and comparing it with a mineral having a known reflectance. Usually using pyrite, galena, beryllium ore and sphalerite as the standard, the minerals to be tested are mounted on the same slide as the standard minerals so that they are as close as possible so that they can be viewed in the same field of view. By comparing the brightness of the two minerals that are inverted each other, you can know whether the reflectivity of the mineral to be tested is higher or lower than the standard mineral. Obviously, this is a qualitative to semi-quantitative method. When the difference between the mineral and the standard mineral reflectivity is large, it is easy to judge the reflectivity of the two. When the mineral to be tested cannot appear in the same field of view as the standard mineral, it can be compared by means of “visual persistence”, that is, first look at a mineral, and save the impression of brightness by eye vision, and the second kind appears in the field of view. The contrast of mineral brightness in the middle.
Using four standard minerals, the reflectivity of various minerals to be tested can be divided into the following five levels:
A reflectance is higher than that of pyrite (R>53%)
B Minerals with reflectivity between pyrite and galena (53%>R>43%)
C Minerals with reflectivity between galena and beryllium ore (43%>R>30%)
D Minerals with reflectivity between beryllium and sphalerite (30%>R>17%)
E Reflectance is lower than that of sphalerite (R<17%)
This method does not require special equipment except the microscope, is simple, easy, fast and effective, so it is widely used in practical work.
The double reflection of minerals is still observed under a single polarizer. For aggregates of the same kind of minerals, it is necessary to carefully observe the change in brightness of different particles to determine whether there is a difference in brightness; for a single particle, it is necessary to rotate the stage to see if the brightness changes. The observations can be divided into 3 levels: visible, visible and absent.
2. Photomultiplier tube method The photomultiplier tube method uses the photoelectric effect to determine the reflectivity of minerals. The phenomenon that a substance emits electrons under the action of light is the photoelectric effect. At this time, the electron released by the substance is called photoelectron, and the current formed in the electric field is called photocurrent. The photomultiplier tube is composed of an anode, a cathode and a plurality of "secondary emission target screens". The light illuminates the cathode to emit photoelectrons, which fall into the "secondary emission target screen" multiple times, generating secondary electrons, which magnify the photocurrent by several million times. At the anode, the output current is measured by a sensitive galvanometer. The basic law of photoelectric effect shows that the number of electrons released by light-irradiated substances is proportional to the intensity of incident light in unit time and unit area. Therefore, as long as the photocurrent intensity of the standard and the mineral to be measured is separately measured, the reflectance of the mineral to be measured can be calculated according to the reflectance of the standard sample. The currently used photomultiplier tube micrometer has a microprocessor for direct reading and printing results.
When using a photomultiplier tube micrometer to measure the reflectivity of a mineral, high sensitivity can be achieved as long as the standard is correct, the quality of the light is good, the level of installation is controlled, the temperature difference is controlled, vibration is avoided, and precise quasi-focus is achieved. Therefore, this method has been defined by the International Commission for Mineral Science as a standard for quantitative determination of mineral reflectance.
(3) Factors affecting reflectivity and double reflection The following factors affect the correct measurement of reflectivity and double reflection, and must be noted.
(1) The intensity of the light source and the wavelength of the incident light have a great influence on the reflectivity. The stronger the light source, the higher the reflectivity; the wavelength changes and the reflectivity changes (see table above). It can be seen that when determining the reflectance, the same test conditions are maintained for the standard and the mineral to be tested.
(2) The polishing quality of the surface of the light sheet should be high, so that there is no scratch, pitting or oxide film, otherwise the reflectivity of the mineral will be lowered. In addition, the light sheet must be strictly flattened. If the surface of the light sheet is not perpendicular to the incident light, it will affect the direction of the reflected light and reduce the reflectivity of the mineral.
(3) Other factors such as immersion medium, magnification, focal length, internal reflection and temperature difference can affect the reflectivity. [next]
Second, the reflection color of the mineral and the reflection polychromaticity (a) the concept of reflection color and reflection polychromaticity The color of the mineral light sheet under the single polarizer is called the reflection color of the mineral. The phenomenon in which the reflected color changes with the orientation of the mineral is called reflection pleochroism. The color of the reflection is different from the color of the mineral specimen when it is observed by the naked eye. It is the "color" caused by the selective reflection of the mineral polishing light directly under the microscope. When the mineral light is reflected by the light of each wavelength in the white incident light, the reflected color of these minerals appears white to gray; when the mineral reflects the light of a certain wavelength, the reflected color shows the wavelength. colour. For example, galena is approximately equivalent to white incident light, so the reflection color of galena is white; while the chalcopyrite has strong light reflection on the yellow band, so the reflection color is yellow.
The reflected color of the mineral can be explained by the reflectance dispersion curve. Reflectance dispersion refers to the phenomenon that the reflectivity of a mineral varies with the wavelength of the incident light. With the wavelength as the abscissa and the reflectance value as the ordinate, the reflectance dispersion curve can be made (see the figure below). It can be seen from the figure that the reflectance curve of natural copper sharply rises in the yellow, orange and red bands, so the reflected color is the composite color of these three colors; the dispersion curve of pyrite increases significantly in the yellow and orange bands, so Light yellow.

(II) Determination of reflection color and reflection chromaticity The measurement of reflection color and reflection chromaticity has two kinds of measurement methods: microscopic observation and instrumental measurement, and there are two kinds of representation methods: qualitative description and quantitative recording.
Qualitative description is to record the color observed by the naked eye in a textual description. For example, the reflection color of galena is described as "white" and pyrite is "light yellow". For reflection polychromaticity, it can be divided into "obvious, visible and no" level 3, in which the first two levels should describe the change of color as much as possible. For example, the reflection of poisonous sand multicolor can be described as: visible (micro blue - Light orange). Because of the many types of transitions in color, and the descriptions often vary from person to person, it is difficult to distinguish them by visuals and to express them with words.
In order to overcome the above difficulties, the principles and methods of colorimetry can be applied to quantify the reflected color of minerals by numbers. In colorimetry, colors are represented by three elements of hue, purity, and brightness. Hue, also called hue, refers to the type of color, which can be expressed by the dominant wavelength (λd) of the reflected light, which is equivalent to the wavelength of the main peak of the reflectance dispersion curve. Purity is also called saturation. It is represented by the symbol Pe. It means the purity of the color. It can be quantified by the ratio of color light to white light. The pure spectrum color is up to 1 (100%), and the purity value becomes smaller as the color becomes lighter, until pure white. The purity is zero. Brightness, also known as brightness, refers to the brightness of a color, expressed as the reflectivity of a mineral under green light (Rvis). [next]

The reflection color of minerals can be expressed by hue (λd), purity (Pe), brightness (Rvis) and chromaticity coordinates (x, y), which are collectively referred to as color index. The above table lists the color index of some minerals, of which Rvis To be determined, λd and Pe can be obtained on the XYZ system standard chromaticity diagram specified by the International Commission on Illumination. The chromaticity coordinates x and y are calculated by:

x=X/(X+Y+Z)
y=Y/(X+Y+Z)

Where X represents red, Y is green, and Z is blue, the so-called three primary colors. Any color light in the visible spectrum can be mixed by the three kinds of color light in a certain ratio. If the light of the three primary colors is mixed in equal amounts, it is white light.
(3) Factors affecting reflection color and reflection chromaticity (1) The intensity and hue of the light source source can affect the reflection color of the mineral. When the light source is weak, the reflected color will be yellowish.
In order to filter out the excess yellow light in the light source, the microscope is equipped with a blue color filter. When adjusting the light source, the white color of galena is used as a standard.
(2) The requirements for the light sheet when the light sheet is measured and the reflectance are similar, the polishing quality of the light sheet is high, and the installation must be correct. When an oxide film is present on the surface of the light sheet, various colors appear, so the light sheet must maintain a fresh and clean surface.
(3) Influence of surrounding minerals The reflection color of minerals refers to the color of reflected light when a mineral appears alone. When two or more minerals of different colors appear together, it interferes with human vision, called the visual color change effect. For example, pyrite is pale yellow when it appears alone under the microscope. If it is combined with white galena, yellow is more obvious; if pyrite is symbiotic with copper-yellow chalcopyrite or golden yellow natural gold, The yellow feature becomes inconspicuous and is even mistaken for white. It can be seen that the visual color change effect should be paid attention to when observing the reflection color of different mineral aggregates.
Third, the internal reflection of minerals (a) the concept of internal reflection When the light is irradiated onto the surface of a mineral light sheet with a certain transparency, in addition to the reflected light, a part of the light can be refracted into the interior of the mineral, if some internal minerals are encountered Interfaces (such as cleavage, fissures, voids, grains, inclusions, etc.), light can be reflected or scattered, a phenomenon known as mineral internal reflection. If the reflected light has no dispersion, it will still be white light. If dispersion occurs, the color can be displayed, which is called the internal reflection color. Internal reflection is also the reflection of light inside the mineral. The internal reflection color is the body color of the mineral, and the aforementioned reflection color is the color of the mineral. The body color and the color of the body complement each other, and the degree of complementarity is closely related to the transparency of the mineral.
Transparent minerals allow a large amount of light to pass through, and the reflected light is extremely weak. Therefore, the reflected color is mostly gray! Grayish black, the color tone is very weak, that is, the purity of the color is small. Due to the large amount of transmitted light, the internal reflection phenomenon is obvious. If the dispersion is significant, it can also exhibit a strong internal reflection color, such as the bright green emerald color of the malachite and the blue color of the blue copper ore. The complementary phenomenon of the reflection color of the transparent mineral and the internal reflection color is generally not obvious, and the color of the mineral observed by the naked eye is the same as or similar to the internal reflection color. [next]
Translucent minerals have strong transmitted and reflected light, so the internal reflection color and reflection color are relatively strong, and the complementary relationship between the two is more obvious. The color of the mineral is inconsistent with the internal reflection color or the reflection color. It is a composite color of the internal reflection color and the reflection color. For example, the hematite is generally brownish red, the reflection color is grayish white with a blue hue, and the inner reflection color is dark red, and the three are different.
Opaque minerals do not allow light to pass through, so no internal reflection occurs. Metallic minerals such as pyrite, chalcopyrite and galena have no internal reflection.
Since the transparency of the mineral is closely related to the reflectivity, the relationship between the internal reflection phenomenon and the reflectance is also very obvious. In general, the higher the reflectivity of minerals, the less obvious the phenomenon of internal reflection.
(2) Determination of internal reflection
Two types of internal reflection are commonly used, oblique measurement and orthogonal polarization. The results of the measurement can be divided into three levels: “obvious, visible and non-existent”. For minerals with internal reflection, the internal reflection color should be further observed and described in parentheses. For example, the internal reflection phenomenon of cinnabar can be recorded as: obvious (red red).
1. Oblique method The light source is obliquely illuminated from the side on the surface of the light sheet so that the reflected light is symmetrically tilted and reflected without entering the objective lens (below). When the light is obliquely directed onto the surface of a transparent or translucent mineral, except for a portion that is obliquely reflected off, the remaining light penetrates into the interior of the mineral, encounters an interface of appropriate inclination, and reflects from the interior of the mineral into the objective lens, so that the microscope field is presented. Brightness and a transparent visual perception, ie internal reflection. If it has a certain color, it means that the mineral has an internal reflection color.

The observation of the internal reflection of minerals by oblique illumination is less sensitive, and only the internal reflection of minerals with significant internal reflection can be observed. Therefore, do not think that the minerals that are black under the mirror when obliquely illuminated must have no internal reflection. In order to improve the observation effect, the mineral powder can be observed by oblique illumination because the light transmittance of the powder is better than that of the bulk mineral. Mineral powder can be obtained by scoring the surface of the light sheet under a microscope with a steel needle or a diamond pen.
2. Orthogonal Polarization Method This method is to observe the internal reflection phenomenon of minerals under orthogonal polarized light. When the incident plane linear polarization is reflected by the mineral surface, the reflected light is substantially linearly polarized, so that it cannot pass through the upper polarizer, and the field of view is dark. However, the case where the linear polarized light incident inside the mineral is reflected is different, because the light waves reflected by the interface inside the mineral are often elliptically polarized or reflected and rotated, that is, a part of the internally reflected light can pass through the upper polarizer. To make the field of view show a certain brightness, which is the phenomenon of internal reflection under orthogonal polarized light.
The effect of mineral powder observation under orthogonal mirror is better. For minerals with very weak internal reflection, oil can also be used as a medium to observe the mineral powder. This is the most effective way to observe internal reflection, because the reflectivity of minerals in oil immersion will be greatly reduced, and the amount of light penetrated into the interior of mineral powder. Greatly increased, making the internal reflection phenomenon more visible.
(III) Factors affecting the measurement of internal reflection (1) Light source Since the internal reflection light is relatively weak, it is necessary to use a strong light source as the incident light. The light source should use white light in order to observe the correct internal reflection color.
(2) Incidence angle When observing the internal reflection of minerals by oblique illumination, the incident angle is preferably 30 ÌŠ to 45 ÌŠ. When observing, the incident angle and direction of the incident light should be changed to seek a favorable reflection angle, increase the amount of light entering the objective lens, and enhance the transparent visual perception under the mirror. [next]
(3) Abrasives Avoid avoiding the color of the abrasive deposited in the cracks and pits of the mineral film as the internal reflection color of the mineral.
(4) Interference phenomenon When white light is obliquely incident on colorless transparent minerals such as quartz and calcite , it may appear as a dispersion like a prism, causing interference, which causes the interior of the mineral to display "color". Do not give this internal reflection strong but The phenomenon of no internal reflection color is mistaken for color reflection.
(5) Objective lens multiple The oblique illumination method can only use a low magnification objective lens or a medium magnification objective lens. Because the working distance of the high magnification objective lens is too short, the light is not allowed to be irradiated onto the surface of the light sheet at a suitable angle. On the contrary, the orthogonal polarization method preferably uses a high power objective lens because the light passing through the high power objective lens has a strong convergence effect, and becomes oblique light of various directions and incident angles, so that the chance of minerals exhibiting internal reflection is increased.
(6) Heterogeneous and polarized color homogeneous minerals can be observed by orthogonal polarization method in any direction, but the heterogeneous minerals show heterogeneity and polarized color under orthogonal mirror, so it should be in the extinction position. Correctly observe internal reflections. To distinguish between the internal reflection color and the polarization color, it is only necessary to rotate the object table. When the mineral orientation is changed, the internal reflection color does not change substantially, and the polarization color changes significantly.
Fourth, the hardness of minerals The hardness of minerals refers to the ability of minerals to resist external mechanical forces. According to the type of mechanical force, the hardness of minerals can be divided into three cases, namely, hardness, abrasion resistance and compressive hardness.
(A) Characterizing the hardness The ability of a mineral to resist the scoring force is called scoring hardness. The method of measuring the mineral scoring hardness under the microscope is simple. The steel needle (sewing needle) and the copper needle (grinded with pure copper wire) are used as tools to score the surface of the mineral. The result is divided into three levels:
(1) High-hardness minerals Minerals that are inscribed with steel needles, such as pyrite and hematite.
(2) Medium hardness minerals can be inscribed with steel needles, but the copper needles can not be moved. Such as chalcopyrite, sphalerite and so on.
(3) Minerals with low hardness minerals carved with steel needles, such as galena and molybdenite .
Under the microscope, the mineral is drawn under a low or medium objective lens, and the angle between the metal needle and the surface of the light sheet is 30 ̊ to 45 较. When you are scribbling, swipe from left to right, not too hard. After scribing, observe whether the surface of the light sheet leaves a mark. It is necessary to avoid mistakenly identifying the dust, dirt, oxide film or the powder of the metal needle itself, which is imprinted on the surface of the light sheet, as a score.
(B) anti-wear hardness The ability of minerals to resist the grinding force is called anti-wear hardness. Microscopic observation of the wear resistance is only to compare the relative hardness of adjacent minerals, but can not quantify or classify the mineral hardness. Although the prepared light sheet is smooth to the naked eye, it can still exhibit unevenness under the microscope. During the polishing and polishing process, the soft minerals are easily worn and relatively concave, and the hard minerals are not easily worn and protruded, forming a slope between the adjacent soft and hard minerals (below). The arrowed lines in the figure indicate the reflected light, and the reflected light is vertically upward in the plane, but the light on the inclined surface is reflected in the direction of the low-hardness mineral, so that the position of the mineral boundary line appears dark, and at the periphery of the boundary line, The light overlaps and appears brighter, creating a "bright line." When the microscope barrel is lowered or the stage is lowered, the focus of the objective lens is raised from the position of B in the figure to the position of A, and the bright line is moved toward the direction of the low-hardness mineral. When the lens barrel or the lifting stage is lowered, the focus of the objective lens also drops, and the bright line moves toward the direction of the high hardness mineral. Thereby the relative hardness of the adjacent minerals can be compared.

Schematic diagram of the reflection of normal incident light on different raised mineral surfaces [next]

During the operation, if the bright line is not obvious, the field of view aperture can be appropriately reduced to improve the sharpness of the bright line. When observing the movement of the bright line, it is advisable to use a method of lifting the lens barrel or lowering the stage. The falling of the lens barrel or the lifting stage makes it easy to hit the objective lens on the light sheet.
(III) Compressive hardness The ability of minerals to resist indentation is called compressive hardness. The compressive hardness is measured by a microhardness tester, and the hardness tester is made of a "pressure head" made of cemented carbide or diamond. When a certain load is applied, the indenter can be pressed out of the mineral surface. The compressive hardness of the mineral can be calculated from the load and the size of the indentation.

Vick indenter (a) and Knopp indenter (b) and their corresponding indentation diagram

Currently, the most commonly used compressive hardness is Vicker hardness, followed by Knoop hardness.
The indenter used for Vickers hardness is a diamond square cone with a cone angle of 136 ̊ (top a). The Vickers hardness value (Hv) is calculated by dividing the load by the surface area of ​​the indentation. The formula is:

P
H _V = ———————————
d ² /[2sin(136 ^o /2)]

=1.854p/d ²

Where p is the load, kg;
d - the diagonal length of the square indentation, mm.
The indenter used for Knoop hardness is a diamond diamond cone. The angle between the two adjacent faces of the cone is 130 ̊ and 172.5 分别, respectively. The indentation is a long diamond (above b), and the Noel hardness value (H) _k ) is calculated as:

P
H _K = ———————————————————
1/2 cot[1/2(172.5 ^o )]tan(130 ^o )d ²

= 14.229p/d ²

Where P is the load, kg;
d - the length of the long diagonal of the rhomboid indentation, mm.
The new microhardness tester is equipped with a computer that directly displays the results. [next]
5. Structure of minerals The structure of minerals refers to the external morphological characteristics and internal microstructure of mineral grains, such as crystal form, cleavage, twin crystal and inner ring zone, etc., all of which have applicative significance.
(I) Crystal Form Since the arrangement of the particles in the crystal follows a certain rule, the ideal crystal has one or several forms fixed. The natural geometric polyhedral shape of the crystal is called the crystal form. Due to the limitation of formation conditions, some crystals are irregular in shape, which is called his crystal; the crystal is partially irregular in shape, while the other part is regular, called semi-automorphic crystal; the regular crystal is called self. Shaped crystal. Self-crystal crystals have a certain effect on the identification of minerals under the microscope, but it should be noted that the crystal morphology seen under the microscope is a plane cut out in a certain direction of the crystal, rather than the shape of the natural crystal plane. For example, the pyrite of cubic crystal shape has a square shape of natural crystals, but the shape of the cut surface may be rectangular, triangular, trapezoidal or the like in addition to a square shape (see the following figure). Therefore, when observing the light sheet, pay attention to the association and restore the three-dimensional crystal form represented by the surface morphology.

(2) Cleavage The intrinsic property of minerals to rupture in a certain direction along the crystal lattice under the action of external force is called cleavage, and the plane along the cleavage is called the cleavage plane. The cleavage is determined by the internal structure of the crystal, and the same crystal has the same type of cleavage. In mineralogy, the cleavage in the same direction is called a group. Some minerals have only one set of cleavage, and some have multiple sets of cleavage. Therefore, cleavage can be used as an auxiliary feature to identify minerals.
According to the difficulty level of cleavage, they can be divided into five levels, from easy to difficult, which are called extreme complete cleavage, complete cleavage, medium cleavage, incomplete cleavage and extremely incomplete cleavage. Microscopically, only complete cleavage and complete cleavage can be observed. It is usually easy to observe after etching the light sheet. The use of incompletely polished light sheet is also conducive to the appearance of cleavage.
The cleavage of some minerals has special identification significance. For example, the {100} three-group cleavage of galena often intersects into a triangle. During the grinding process, the cleavage junction is easily peeled off into a triangular cavity, which is represented by a black triangle under the microscope. A hole having a characteristic (3) twin crystal of two or more regular crystals formed by a certain symmetry law, called a twin crystal. According to the way in which twins are continuous, the twins can be divided into two categories. The twin crystals formed by the interpenetration of crystals are called interpenetrating twins; if the twins do not interpenetrate, but are joined together by simple planar contact, they are called contact twins. The contact twin crystal can be further classified into a simple contact twin crystal, a polycrystalline twin crystal, and a cyclic twin crystal.
In the twin crystal, the corresponding crystal faces and crystal edges of two adjacent single crystals are generally not parallel to each other. Therefore, under the orthogonal polarizer or after etching, since the orientation of each single crystal is different, the extinction orientation and the degree of acceptance of etching are also different, and a phenomenon of light and dark may occur.
(4) Inside the grain of some minerals, there are a series of annular lines and strips along the crystal plane. These bands are represented by reflectivity, reflection color, hardness, chemical composition, impurity inclusions and porosity. The differences in other aspects have certain identification significance. For example, pyrite containing cobalt and nickel often exhibits a band of light rose (cobalt-containing) and a purple (nickel-containing) hue with a yellow-white (no impurity) band.
The inner band structure of the mineral grains is mainly generated during the mineral formation process due to the composition of the medium and the environment in which it is located. Specifically, the endless belt structure may be formed by crystallization of a melt or a solution and recrystallization of a colloidal substance.
6. Identification of mineral etching (I) Concept of etching identification Etching identification refers to a method of etching mineral polishing surface by using certain chemical reagents to identify minerals according to etching reaction. The etching reaction can be divided into two categories according to the results: when the reagent does not react with the mineral, it is called a negative reaction, and when the reagent reacts with the mineral, it is called a positive reaction. Positive reactions have the following different performances:
(1) Explicit structure The reagent dissolves the amorphous film on the surface of the light sheet, so that the light sheet exhibits the cleavage pattern, crack, double crystal grain, internal ring structure of the grain, and grain boundary. This phenomenon is collectively referred to as "explicit structure."
(2) Blackening After the surface of the mineral is etched by the reagent, it becomes rough and uneven. When the incident light is reflected, it becomes scattered light, and the etched area becomes grayish black to black under the microscope. This phenomenon is called "blackening."
(3) Dyeing When the reagent dissolves the mineral, a precipitate is formed by a chemical reaction, and remains in the etched portion in the form of a colored film. This phenomenon is called "dyeing", such as dyeing blue, yellowing, and the like. [next]
(4) Halo If the precipitate is a fine crystal with five colors, it can make various interference colors when reflecting light waves, just like a rainbow. This phenomenon is called blooming.
(5) Halo The reagent drops on the mineral surface, sometimes causing a color change around the droplet, which is called “halo” or “smudge”. This phenomenon is caused by a gas that is diffused outward from the reagent droplets, and is a relatively special etching reaction phenomenon.
(6) Foaming A chemical reaction between a reagent and a mineral to cause gas to escape is called "foaming" or "foaming".
In addition, when the reagent droplets do not appear "halo" around, and the fine water droplets are agglomerated, it is called "sweat circle". This phenomenon is a negative reaction.
(II) Reagents, tools and operations for etching identification Generally, six standard reagents are used for etch identification, which are 1:1HNO ₃ , 1:HCI, 20% KCN, 20% FeCl ₃ , 5% HgCl ₂ and 40% KOH. . If necessary, 3% H ₂ O ₂ and aqua regia (3 parts concentrated HCL and 1 part concentrated HNO ₃ ) may also be used. Note that KCN is highly toxic in the above reagents.
The tools for etch identification are simple, mainly for vials, droppers, platinum drops, and filter paper.
Etch identification is performed as follows:
(1) Wipe the light sheet and place it under the microscope. Find the mineral particles to be identified with a low or medium objective.
(2) Drop the reagent on the end of the platinum drip rod washed with distilled water with a dropper, and then send the reagent to the mineral surface.
(3) Observe the reaction between the reagent and the mineral within 1 min.
(4) Immediately after 1 min, the etched area was washed with distilled water, and the dry cleaning liquid was sucked with filter paper, and then observed whether there was any obvious structure, blackening, staining, blooming, halo, and the like.
(III) Factors affecting the identification of erosion In order to obtain the correct identification results, the following influencing factors should be noted:
(1) The smooth surface of the light sheet must be clean and free of dirt such as oil, dust or clay to ensure that the reagent reacts directly with the mineral.
(2) Reagents KCN, FeCl ₃ , HCl ₂ and KOH are easily evaporated and produce precipitates, which are colored under the microscope and should not be mistaken for positive reactions. These precipitate films disappear as long as they are rinsed with distilled water.
(3) Electrochemical action When the mineral particles are small and a drop of the reagent is dropped on the two minerals, the current is generated by the potential difference, and the reaction of one of the minerals is strengthened, and the reaction of the other mineral is weakened. Therefore, the identification of the etch is to select mineral particles larger than the droplets of the reagent.
(4) Impurities and cracks The positive reactions such as foaming of the tested minerals appear uniformly in the surface. If the reaction appears linearly, it is mostly caused by impurities in the veins or in the cracks. Pay attention to the difference. In addition, the mineral isomorphism in the mineral also affects the results of the erosion identification.
(5) The ore genesis are the same kind of minerals, and the geological effects are different, and the etching reaction may also be different. For example, the chalcopyrite and beryllium ore in the primary ore react negatively with nitric acid, but the chalcopyrite and beryllium ore in the oxidized ore often react positively with nitric acid.
7. Other Identification Characteristics of Minerals (I) Magneticity Magnetic properties are an important property of metal minerals. They are the basis for magnetic separation of minerals. However, the use of magnetic properties to identify minerals under a microscope has significant limitations and is usually only aided in identifying significance.
There are two methods for measuring magnetism under the microscope. One is scribed hardness measurement, carved down to a powder, with the magnetized needle detecting whether magnetic. Note that the magnetized steel needle cannot directly contact the powder, but the needle tip is close to the powder to see if the powder automatically jumps onto the magnetic needle. If the tip of the needle touches the powder directly, the powder is fine, and the non-magnetic powder can be adhered to the needle tip due to the adsorption. Another method of measuring magnetism is to use a pin to suck the round head onto the magnet and perpendicular to the plane of the magnet. The hand held magnet attracts the tip of the pin to the mineral to be tested. If the mineral is magnetic, the tip of the needle will be biased toward the mineral. This method is less sensitive to weak magnetic minerals.
(B) Conductivity Conductivity refers to the ability of minerals to conduct current. The conductivity of minerals detected under the microscope can only be carried out on larger particles. The method is to use a universal meter or an ohmmeter, and put a sharp needle on the test pen to test the resistance of the mineral surface. The distance between the two test leads is preferably 1 mm. It should be noted that the test pen cannot be placed on 2 minerals or 2 particles separated by fissures, otherwise the test results are incorrect.
The conductivity of minerals can be classified into three categories depending on the size of the resistor. A conductive mineral (such as red arsenic ore) with a resistance of less than 10-6 Ω, a weakly conductive mineral (such as galena) with a resistance of 10-6-10-2 Ω, and a non-conductive mineral with a resistance of more than 10-2 Ω. (such as sphalerite).
(III) Brittleness and plasticity Under the action of external force, the properties of mineral fracture and deformation are called brittleness and plasticity. Brittle minerals are easily broken after being pressed, and appear as crushed structures under the microscope. For example, pyrite is often crushed. When scribing brittle minerals, rough marks and granulated powder are produced, and the powder is bouncing off the mineral, and no plastic bulge occurs on both sides of the score. Plastic minerals are not easily broken under pressure, but deformed. Under the microscope, they appear as wrinkled structures. For example, galena is often wrinkled, and rows of curved black triangle holes are visible. When the plastic mineral is scored, the powder is extremely small, and even if it is not in the form of an equiaxed grain, it is in the form of a sheet or a strip, and the powder has no bouncing feeling when it is separated from the mineral. The nicks left behind are smoother and the sides are slightly raised due to plastic deformation.
It has been suggested to classify the brittleness and plasticity of minerals by measuring the minimum load at which the Vickers hardness value begins to produce cracks. It has also been proposed to use the reciprocal of the diagonal length of the indentation as the standard for measuring the brittleness and plasticity of the mineral.

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