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, not being rock-forming, usually accompany certain rocks, being a source of valuable raw materials. Below we will consider the main properties of sulfides and compounds close to them, and also pay attention to the areas 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 derivatives of hydrogen sulfide, they are all included in the class of sulfides due to the similarity of properties.
Characteristic for minerals of this class chemical bond is covalent, withmetal component. The most common structures are coordination, island (cluster), sometimes layered or chain.
Physical properties of sulfides
Practically all sulfides are characterized by high specific gravity. The value of hardness on the Mohs scale for different members of the group varies widely and can range from 1 (molybdenite) to 6.5 (pyrite). However, most sulfides are quite soft.
With a few exceptions, cleophane is a kind of zinc blende or sphalerite, minerals of this class are opaque, often dark, sometimes bright, which serves as an important diagnostic feature (as well as shine). Reflectivity can range from medium to high.
Most sulfides are minerals with semiconductor electrical conductivity.
Traditional classification
Despite the commonality of basic physical properties, sulfides, of course, have external diagnostic differences, according to which they are divided into three types.
- Pyrites. This is the collective name for minerals from the group of sulfides, which have a metallic luster and a color that has shades of yellow or yellow tint. The most famous representative of pyrite is pyrite FeS2, also known as sulfur or iron pyrite. They also include chalcopyrite CuFeS2 (copper pyrite), arsenopyrite FeAsS (arsenic pyrite, aka talheimite or mispikel), pyrrhotite Fe7S 8 (magnetic pyrite, magnetopyrite) andothers.
- Glitter. This is the name given to sulfides with a metallic luster and color from gray to black. Typical examples of such minerals are galena PbS (lead luster), chalcocite Cu2S (copper luster), molybdenite MoS2, antimonite Sb 2S3 (antimony sheen).
- Fakes. 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 blend). Also known are the realgar As4S4 - red arsenic blende, and orpiment As2S 3 - yellow arsenic blende.
Differences in chemical characteristics
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). Examples of such minerals include galena, sphalerite, and cinnabar. They are all simple derivatives of hydrogen sulfide.
- Double sulfides differ in that several (two or more) metal cations bind with the sulfur anion. These are chalcopyrite, bornite (“variegated copper ore”) Cu5FeS4, stannin (tin pyrite) Cu2 FeSnS4 and other similar compounds.
- Disulfides are compounds in which cations are bonded to the anionic group S2 or AsS. These include minerals from the group of sulfides and arsenides (sulfoarsenides), such as pyrite,the most common, or arsenic pyrite arsenopyrite. Also included in this subclass is cob altin CoAsS.
- Complex sulfides, or sulfos alts. This is the name of minerals from the group of sulfides, arsenides and compounds close to them in composition and properties, which are s alts of thioacids, such as thiomarsenic H3AsS3, thiobismuth H3BiS3 or thioantimony H3SbS3. Thus, the subclass of sulfos alts (thios alts) includes the mineral lillianite Pb3Bi2S6 or the so-called Fahlore Cu3(Sb, As)S3.
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. Layered sulfides have flattened tabular or foliated crystals, such as orpiment or molybdenite.
Cleavage of sulfides can be different. It varies from very imperfect in pyrite and imperfect in chalcopyrite to very perfect in one (orpiment) or several (sphalerite, galena) directions. The type of fracture is also not the same for different minerals.
Genesis of sulfide minerals
Most sulfides are formed by crystallization from hydrothermal solutions. Sometimes the minerals of this group have a magmaticor skarn (metasomatic) origin, and can also be formed during exogenous processes - under reducing conditions in zones of secondary enrichment, in some cases in sedimentary rocks, like pyrite or sphalerite.
Under surface conditions, all sulfides, except for 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 the processes of changing sulfides are such types of minerals as oxides, halides, carbonates. In addition, due to their decomposition, the formation of native metals - silver or copper.
Features of occurrence
Sulfides are minerals that form ore accumulations of different nature depending on their ratio with other minerals. If sulfides predominate over them, it is customary to speak of massive or continuous sulfide ores. Otherwise, the ores are called disseminated or veinlet.
Very often sulfides are deposited together, forming deposits of polymetallic ores. Such, for example, are copper-zinc-lead sulfide ores. In addition, different sulfides of one metal often form its complex deposits. For example, chalcopyrite, cuprite, bornite are copper-bearing minerals that occur together.
Most often, the ore bodies of sulphide deposits are in the form of veins. But there are also lenticular, stock, reservoir forms of occurrence.
Use of sulphides
Sulfide ores are extremely important as a source ofrare, precious and non-ferrous metals. Copper, silver, zinc, lead, molybdenum are obtained from sulfides. Bismuth, cob alt, nickel, as well as mercury, cadmium, rhenium and other rare elements are also extracted from such ores.
Besides this, some sulfides are used in the production of paints (cinnabar, orpiment) and in the chemical industry (pyrite, marcasite, pyrrhotite - for the production of sulfuric acid). Molybdenite, in addition to being used as an 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 analogues in the form of single crystals.
Another area where sulfides find application is the radioisotope geochronological dating of certain ore rocks using the samarium-neodymium method. Such studies use chalcopyrite, pentlandite and other minerals containing rare earth elements - neodymium and samarium.
These examples show that the scope of sulfides is very wide. They play an essential role in various technologies both as raw materials and as independent materials.
