Civil Engineering Reference
In-Depth Information
Quartz is almost pure silicic dioxide and the hardest of the ordinary minerals.
It is the main constituent of glass and silica and an important ingredient in
Portland cement. Pure quartz is as clear as water and is known as rock crystal.
Normal quartz is unclear and white or grey, and is a part of granite, sandstone or
quartzite, or the sand of these rock types.
Pure limestone is a monomineral rock type of the mineral calcite. Accessible
sources of limestone appear as veins or formations in many different types of
rocks of different ages.
Limestone is used in a variety of products - it is one of the most important con-
struction materials in the world after sand, gravel and crushed stone. The largest
consumer of limestone is the cement industry. Cement nowadays means
Portland cement, which is produced from a mixture of two thirds ground lime-
stone, clay, iron oxide and a little quartz, heated to 1500°C. Gypsum is added to
the mixture and then it is ground to a fine cement.
Limestone is an important filler in industries producing plastics, paint, var-
nish, rubber and paper. Some limestone is used in the production of glass and
fibreglass to make the material stronger. In the metal industry, limestone is used
to produce slag.
As well as quartz and limestone, there are many non-metallic minerals of
rather more limited use. Important minerals are gypsum, used in plasterboard
and certain cements, potassium chloride and sodium chloride, which form the
base of a whole series of building chemicals, partly in the plastics industry, and
kaolin, used as a filler in plastic materials and paints. Asbestos, which was wide-
ly used earlier this century, is now more or less redundant as a result of its health
damaging properties.
Generally, the energy consumption and polluting potential of non-metallic
minerals are much lower than in the metal industries, and their resources are
generally richer.
Extraction of the minerals usually takes place in a quarry, where stones with
the lowest impurity content are cut out as blocks, broken down and ground. In a
few cases, the minerals can be found lying on the surface. One important exam-
ple of this is quartz sand.
Extraction uses large quantities of material, causing large scars on the land-
scape. As with the metallic ores, serious damage can be caused to local ecosystems
and ground water which can be quite difficult to restore later. Certain minerals
such as lime and magnesium can be extracted by electrolysis from the sea, where
the direct environmental impact is somewhat less.
Minerals from the sea
Apart from H 2 O, the main constituents of sea water are the following (in g/kg water): chlo-
rine (Cl) 19.0, sodium (Na) 10.5, sulphate (SO 4 ) 2.6, magnesium (Mg) 1.3, calcium (Ca)
0.4 and potassium (K) 0.4. Blood has a somewhat similar collection of minerals.
Search WWH ::




Custom Search