Silica

Highley, D.E.

Silica

Highley, D.E.. 1977 Silica. London, UK, HMSO, 67pp. (Mineral Dossier No. 18)

Before downloading, please read NORA policies.

Preview

Text
B02700.pdf
Download (5MB) | Preview

Abstract/Summary

Silica crystallises in several forms, the most common polymorph being quartz which occurs abundantly in nature as a major rock-forming mineral. The other principal crystalline forms of silica are tridymite and cristobalite, which, although uncommon in nature, are present in commercially fired products as they are produced by heating quartz at high temperatures. Micro-crystalline forms of silica are not covered by this report. The principal commercial sources of silica in the United Kingdom are `silica sands' and `silica rock'. Silica or quartz sands are produced from sand and weakly cemented sandstone deposits ranging from Carboniferous to Holocene (Recent) in age. Production is, however, mainly confined to a few superior quality sands, notably those of Pleistocene age in Cheshire and of Lower Cretaceous age in Norfolk, Surrey, Kent and Bedfordshire. Holocene sands and Carboniferous sandstones are also locally very important. Silica sand is used principally for foundry moulding purposes and in glassmaking, about 3.3 million and 2.2 million tonnes, respectively, being produced for these purposes in 1975, representing about 90 per cent of the total output. Silica sands have numerous other industrial applications which are based not only on chemical purity but also the physical properties of the sand, such as grainsize distribution and grain shape. Silica rock is produced from hard, compact quartzitic sandstones and quartzites and is used in the manufacture of silica refractories, principally silica bricks. There has been a very marked decline in the production of silica rock in the United Kingdom since the Second World War due to changes in refractory and steelmaking technology and the output of silica rock in 1975 was only 42,000 tonnes compared with 625,000 tonnes in 1949. Silica rock production is now confined to Carboniferous quartzites and quartzitic sandstones in South Wales with one remaining operation in Durham. Both silica sand and silica rock are won by opencast quarrying, the one exception being the Loch Aline mine in north-west Scotland where a bed of high purity sandstone, underlying Tertiary basalts, is mined by pillar and stall techniques. Processing of silica sands is of varying complexity and for most foundry sands and sands used in the manufacture of flat glass and coloured glass, consists largely of washing and sizing. Sand of purity sufficiently high for the manufacture of colourless glass without significant processing is rare in the United Kingdom, the only suitable deposit being that at Loch Aline in Scotland. Elsewhere the sand has to undergo extensive processing involving acid leaching and froth flotation. The United Kingdom is nearly self-sufficient in silica sand and imports, which amounted to 145,000 tonnes in 1976 with a cif value of £1,535,000, came principally from Belgium and comprised high quality glass sand. The United Kingdom exported 54,000 tonnes of silica sand in 1976 with a cif value of £548,000. Imports and exports of quartz and quartzite are small, amounting to 3,600 tonnes valued at £612,000 and 328 tonnes valued at £24,000, respectively, in 1976. Silica sand production in the United Kingdom is dominated by one company, British Industrial Sand Limited, which accounts for over 70 per cent of foundry and glass sand production. There are a significant number of other producers, the largest being Hinckley's Limited, Pilkington Brothers Limited, Sand Developments (UG Glass Containers) Limited, Buckland Sand and Silica Company Limited and Tilling Construction Services Limited. The silica rock quarrying industry is now a fraction of its former size and consists of only six small operations.

Item Type:

Publication - Report

Programmes:

BGS Programmes > Economic Minerals

ISBN:

0115108424

Funders/Sponsors:

Institute of Geological Sciences

Additional Keywords:

Mineral, Silica

NORA Subject Terms:

Earth Sciences