Basalt

Basalt

BASALT (from the Latin words "basaltes", "basanites", from the Greek word "basanos" (testing stone); according to the other version, from the Ethiopian word "basal" (iron-containing stone) * EN: basalt, basaltic rocks; DE: Basalt; FR: basalte; ES: basalto; RU: базальт) is the effused cenotypal basic rock, the effusive analogue of gabbro. The coloration of basalt is dark to black. It consists mainly of the basic plagioclase, monoclinic pyroxene, olivine</>, volcanic glass, and accessory minerals, namely, magnetite, ilmenite, apatite, and others. The structures of basalt are intersertal, aphyric, less often hyalopilitic, the textures are solid or porous, amygdaloidal. Depending on the size of the grain, they distinguish: dolerite is most coarsely grained, anamesite is tiny grained, basalt proper is fine grained. The paleotypal analogues of basalt are the diabases.

The average chemical composition of basalt according to P.Daly (%) is: SiO2 is 49.06; TiO2 is 1.36; Al2O3 is 15.70; Fe2O3 is 5.38; FeO is 6.37; MgO is 6.17; CaO is 8.95; Na2O is 3.11; K2O is 1.52; MnO is 0.31; P2O5 is 0.45; H2O is 1.62. The content of SiO2 within basalt ranges from 44% to 53.5%. They distinguish according to their chemical and mineral composition the olivinic basalts, which are non-saturated with silica (SiO2 is approximately 45%), and the tholeiitic basalts, which are olivine-less or with non-significant content of olivine, but are slightly over-saturated with silica (SiO2 is approximately 50%). The physical-mechanical properties of basalt are very various, which is explained by the varying porosity. The basaltic magmas, having low viscosity, are easily movable, and are characterized by the variety of the forms of embedment (covers, flows, dikes, tabular depositions). There is characteristic for basalt the columnar, less often ball-shaped separateness. The olivinic basalts are known on the bottom of the oceans, on the oceanic islands (Hawaii), and are widely developed within the folded belts. The tholeiitic basalts occupy the vast areas on the tectonic plates (the trappous formations of the Siberia, South America, India). There are associated with the rocks of the trappous formation the deposits of the ores of iron, nickel, platinum, Iceland spar (Siberia). There is known within the amygdaloidal basaltic porphyrites of the region of the Lake Superior within the USA the deposit of the native copper.

The density of basalt is 2520-2970 kilograms per cubic metre. The coefficient of porosity is 0.6-19%, the water absorption is 0.15-10.2%, the compressive strength is 60-400 megapascals, the resistance to abrasion is 1-20 kilograms per square metre, the temperature of the melting point is 1100-1250 degrees Celsius, sometimes up to 1450 degrees Celsius, the specific heat capacity is 0.84 joules per kilogram-kelvin at 0 degrees Celsius, the Young's modulus is (6.2-11.3) • 10^4 megapascals, the shear modulus is (2.75-3.46) • 10^4 megapascals, the Poisson's ratio is 0.20-0.25. The high strength of basalt and relatively low temperature of the melting point have caused its usage as the building stone and the raw material for the stone casting and mineral wool. Basalt is widely used for the obtainment of the crushed gravel, road (curb stone and paving stone) and facing stones, acid-resistant and alkali-resistant material. The requirements of the industry for the quality of basalt as the raw material for the crushed gravel are the same as for the other erupted rocks.

The basaltic separateness

For the production of the mineral wool, basalt is usually used within the blending. It is determined, that the temperature of the melting point of the raw material must not exceed 1500 degrees Celsius, and the chemical composition of the melt is regulated by the following limits (%): SiO2 is 34-45, Al2O3 is 12-18, FeO is up to 10, CaO is 22-30, MgO is 8-14, MnO is 1-3. The stone-casted materials of basalt have the high chemical resistance, hardness and resistance to abrasion, high dielectricity, and are used in the form of the plates for the floors and facing, for the lining of the pipelines, cyclones, and also as the various insulators.

Within the USSR, there have been explored for the crushed gravel the 50 deposits with the industrial reserves of 40 million cubic metres. Two deposits of basalt with the industrial reserves of 6.5 million cubic metres have been explored for the facing stone (Armenian SSR, Georgian SSR). The annual extraction of basalt is more than 3 million cubic metres. Within the USSR, the deposits of basalt are concentrated mainly within the Armenia, Eastern Siberia, and at the Far East. The basaltic covers within the eastern regions of the USA form the large deposits within the New York, New Jersey, Pennsylvania, Connecticut (the largest quarries and stone crushing plants) states.