Hydrogen sulfide is one of the main volatile components of magma. Actively interacting with metals, it forms many compounds. Derivatives of hydrogen sulfide are represented in the earth's crust by more than 200 minerals - sulfides, which, while not rock-forming, usually accompany certain rocks, being a source of valuable raw materials. Below we consider the main properties of sulfides and related compounds, and also pay attention to the scope of their use.
General characteristics of composition and structure
More than 40 elements of the periodic table (usually metals) form compounds with sulfur. Sometimes, instead of it, arsenic, antimony, selenium, bismuth, or tellurium are present in such compounds. Accordingly, such minerals are called arsenides, antimonides, selenides, bismuthides and tellurides. Together with hydrogen sulfide derivatives, all of them are included in the class of sulfides due to the similarity of properties.
The chemical bond characteristic of the minerals of this class is covalent with a metal component. The most common structures are coordination, island (cluster), sometimes layered or chain.
Physical properties of sulfides
Almost all sulfides are characterized by a high specific gravity. The hardness value on the Mohs scale for various representatives of the group varies widely and can range from 1 (molybdenite) to 6.5 (pyrite). However, most sulfides are fairly mild.
With few exceptions, glueophane is a type of zinc blende or sphalerite, minerals of this class are opaque, often have a dark, sometimes bright color, which serves as an important diagnostic sign (as well as shine). Their reflectivity can range from medium to high.
Most sulfides are minerals with semiconductor electrical conductivity.
Traditional classification
Despite the commonality of the basic physical properties, sulfides, of course, have external diagnostic differences, according to which they are divided into three types.
- The pyrites. This is the collective name of minerals from the group of sulfides, which have a metallic luster and color, which has shades of yellow, or yellow discoloration. The most famous representative of pyrites is pyrite FeS 2 , which is also sulfur or iron pyrites. They also include chalcopyrite CuFeS 2 (pyrite sulphide), arsenopyrite FeAsS (arsenic pyrites, also known as talhemit or mispickel), Fe 7 S 8 pyrrhotite (magnetic pyrite, magnetopyrite) and others.
- Glitters. So called sulfides with a metallic sheen and color from gray to black. Typical examples of such minerals are galenite PbS (lead gloss), chalcosine Cu 2 S (copper gloss), molybdenite MoS 2 , antimonite Sb 2 S 3 (antimony gloss).
- Cheating. This is the name of minerals from the group of sulfides, characterized by non-metallic luster. Typical examples of such sulfides are sphalerite ZnS (zinc blende) or cinnabar HgS (mercury blende). The realgar As 4 S 4 is also known - red arsenic blende, and the auripigment As 2 S 3 - yellow arsenic blende.
Chemical differences
A more modern classification is based on the characteristics of the chemical composition and includes the following subclasses:
- Simple sulfides are compounds of a metal ion (cation) and sulfur (anion). As an example of such minerals, we can mention galena, sphalerite, cinnabar. All of them are simple derivatives of hydrogen sulfide.
- Binary sulfides are distinguished by the fact that several (two or more) metal cations are bound to the sulfur anion in them. These are chalcopyrite, bornite (mottled copper ore) Cu 5 FeS 4 , stannine (tin pyrite) Cu 2 FeSnS 4, and other similar compounds.
- Disulfides are compounds in which cations are bonded to the anionic group S 2 or AsS. These include minerals from the group of sulfides and arsenides (sulfoarsenides) such as pyrite, which is the most abundant, or arsenic pyrite, arsenopyrite. Also in this subclass is cobaltin CoAsS.
- Complex sulfides, or sulfosalts. This is the name of minerals from the group of sulfides, arsenides, and compounds similar to them in terms of composition and properties, which are salts of thio acids, such as thi arsenic H 3 AsS 3 , thiobismuth H 3 BiS 3, or thiosimonous H 3 SbS 3 . So, the subclass of sulfosalts (thiosols) includes the lillianite mineral Pb 3 Bi 2 S 6 or the so-called faded ores Cu 3 (Sb, As) S 3 .
Morphological features
Sulfides and disulfides can form large crystals: cubic (galena), prismatic (antimonite), in the form of tetrahedrons (sphalerite) and other configurations. They also form dense, granular crystalline aggregates or phenocrysts. Sulfides with a layered structure have flattened-tabular or leafy crystals, for example, auripigment or molybdenite.
Cleavage of sulfides can be different. It varies from very imperfect in pyrite and imperfect in chalcopyrite to very perfect in one (auripigment) or several (sphalerite, galena) directions. The type of fracture is also different for different minerals.
The genesis of sulfide group minerals
Most sulfides are formed by crystallization from hydrothermal solutions. Sometimes minerals of this group are of magmatic or skarn (metasomatic) origin, and can also be formed during exogenous processes - under reducing conditions in secondary enrichment zones, in some cases in sedimentary rocks such as pyrite or sphalerite.
Under surface conditions, all sulfides, except cinnabar, laurite (ruthenium sulfide) and sperrylite (platinum arsenide), are very unstable and subject to oxidation, which leads to the formation of sulfates. The result of processes of sulfide changes are such types of minerals as oxides, halides, carbonates. In addition, due to their decomposition, the formation of native metals - silver or copper is possible.
Features of occurrence
Sulphides are minerals that form ore clusters of a different nature depending on their ratio with other minerals. If sulfides prevail over them, it is customary to talk about massive or continuous sulfide ores. Otherwise, the ores are called disseminated or streaky.
Very often sulfides are deposited together, forming deposits of polymetallic ores. Such, for example, copper-zinc-lead sulfide ores. In addition, different sulfides of the same metal often form its complex deposits of it. For example, chalcopyrite, cuprite, and bornite are copper-containing minerals that occur together.
Most often, the ore bodies of sulfide deposits have the form of veins. But there are also lenticular, stock, stratum forms of occurrence.
The use of sulfides
Sulphide ores are extremely important as a source of rare, noble and non-ferrous metals. Copper, silver, zinc, lead, and molybdenum are obtained from sulfides . Bismuth, cobalt, nickel, as well as mercury, cadmium, rhenium and other rare elements are also extracted from such ores.
In addition, some sulfides are used in the manufacture of paints (cinnabar, auripigment) and in the chemical industry (pyrite, marcasite, pyrrhotite - for the production of sulfuric acid). Molybdenite, in addition to being used as ore, is used as a special dry heat-resistant lubricant.
Sulfides are minerals of interest due to their electrophysical properties. However, for the needs of semiconductor, electro-optical, infrared-optical technology, not natural compounds are used, but their artificially grown analogs in the form of single crystals.
Another area where sulfides are used is the radioisotope geochronological dating of some ore rocks using the samarium-neodymium method. Such studies use chalcopyrite, pentlandite and other minerals containing rare earth elements - neodymium and samarium.
These examples indicate that the scope of sulfides is very wide. They play a significant role in various technologies both as raw materials and as independent materials.