Sodium chloride (commonly known as salt) is a colourless crystalline compound with the formulae NaCl. It occurs naturally as the mineral halite and in sea water. Research Sodium Chloride
Boracite is a mineral of a white or grey colour occurring massive and in isometric crystals. It has the formulae Mg3B7O13Cl and a relative hardness of 7. It occurs associated with beds of halite, anhydrite, and gypsum and is formed by the evaporation of bodies of salt water. Research Boracite
Polyhalite has the formulae KaCa2Mg(SO4)4ù2H2O and a relative hardness of 4. It is a source of potassium and occurs in bedded deposits associated with sylvite, carnallite, halite, and has a characteristic red colour. Research Polyhalite
Sedimentary rock is a deposit that has been laid down by water, wind, ice, or gravity. The material of which sedimentary rocks are composed has usually been transported from its source. They have accumulated at or near the Earth' s surface at normal temperatures and pressures, and are thus distinguished from igneous rocks, which have originated as magma in a molten or semi- molten state, and from metamorphic rocks, which have been produced by the effects of heat or pressure. Many sedimentary rocks were deposited in water in which the transported material was in a state of suspension or solution. After deposition they have been consolidated. Some, such as loess, were deposited by the wind; some, such as boulderclay, are the result of glacial action; some have simply accumulated in place. Sediments can be divided into three groups: clastic rocks, chemical precipitates, and organic sediments. Of these, clastic sediments are the most abundant. They are made up of fragments of pre-existing rocks. Clays, sands, and gravels are in this category.
Chemical precipitates include some limestones (the English Chalk, for example) and deposits formed by the evaporation of lakes or seawater. These deposited rocks include gypsum and halite. Organic sediments are those formed largely of the remains of once-living organisms: examples are coal, oil shale, and limestones made mainly of fossil material.
By volume, sedimentary rocks make up only five per cent of the known crust of the Earth, compared with 95 per cent of igneous rocks. They are, however, exposed on over two-thirds of the Earth's land surface, forming thin but extensive deposits. The commonest types are shales, sand-stones, and limestones. The earliest known sedimentary rocks came from the Barberton Mountain Land of South Africa; these have been dated as 3,500 million years old. Research Sedimentary Rock
Sylvite (sylvine) is an industrial mineral, the naturally occurring potassium chloride, and as such the main mineral ore of potassium. Sylvite has a relative hardness of two and is used as a fertilizer. Sylvite is an evaporate mineral found in sedimentary evaporate deposits such as dried-out saltlakes and seas in deserts, and is associated with halite. Sylvite was confirmed as a distinct species of mineral in 1832 but was known at least during the 17th century. Research Sylvite
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Sodium Chloride
