USEFUL MINERALS. 



STRICTLY speaking, a mineral is an inorganic 

 body with a more or less definite chemical 

 composition, and having a regular geometric form 

 in which it crystallises. This, at least, is the case 

 with the great majority of minerals. A mass of 

 rock may be composed either of one or of several 

 minerals ; thus, quartz rock is formed of the single 

 mineral quartz, and granite rock is formed of the 

 three minerals, quartz, felspar, and mica. There is, 

 therefore, a distinction between the terms ' rock ' 

 and ' mineral ;' but we shall here use the latter 

 term in the wider sense in which it includes all 

 inorganic substances that is, all substances 

 except those derived from the vegetable and 

 animal kingdoms. Only the non-metallic minerals, 

 however, or what are usually classed as such, 

 will be treated of in this sheet, metallic ores and 

 metals forming the subject of a separate number. 

 On account of extensive discoveries in new local- 

 ities of many valuable minerals, of the profitable 

 applications of some formerly regarded as useless, 

 and of the possible exhaustion before long, in this 

 country at least, of others, such as coal, mineral 

 products have, for the last twenty years, been 

 gradually acquiring an interest and importance 

 greater than they ever possessed at any former 

 period. 



The various kinds of rock, and the way in which 

 they occur in the crust of the earth, are described 

 in the number on GEOLOGY ; but we may here 

 briefly state what the three principal classes of 

 them are : 1st, We have aqueous, sedimentary, or 

 stratified rocks, which have been deposited under 

 water, and lie in parallel beds or strata. These 

 include, among others, sandstones, limestones, 

 coal, and shale, id, Igneous or unstratified rocks, 

 which are of volcanic origin, and have no true bed- 

 ding. Of these, lava, basalt, dolerite, and porphyry 

 arc examples. And ^d, Metamorphic rocks, which 

 may either be of aqueous or igneous origin, but 

 whose former condition has been changed by heat 

 and chemical action. Such rocks as gneiss, mica- 

 schist, serpentine, and some granites are of this 

 class. The sedimentary series are the only rocks 

 that contain the remains of plants and animals, 

 called fossils, which are of great importance in 

 determining the geological age of the different 

 groups of strata termed formations. All three 

 divisions of rocks are found traversed by veins 

 and lodes of sparry minerals and metallic ores ; 

 while other minerals, such as coal and clay-band 

 ironstone, are only found in stratified formations, 

 and are themselves real beds of sedimentary rock. 



BITUMINOUS SUBSTANCES. 



Under this head, we shall take the more import- 

 ant natural bitumens, such as asphalt, petroleum, 

 and naphtha; but it is well to state that the 

 varieties of this substance are numerous, and all 

 are valuable as sources of light and heat They 

 consist essentially of carbon and hydrogen ; burn 

 in the open air with a highly smoky flame ; and 

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are probably the result of the action of subter- 

 ranean heat on coal or lignite. In this section, 

 too we shall include coal, lignite, jet, bituminous 

 shale, and other allied bodies ; because, although 

 bitumen does not appear to exist in them ready 

 formed, yet, on being distilled in close vessels, 

 they yield products similar to the native bitumens. 

 Such minerals are more properly called bitumin- 

 iferous than bituminous. The word bitumen is 

 from a Greek term signifying the pitch-tree. 



CVw/. No product of the mineral kingdom is of 

 greater importance to man than coal. Its value 

 as a fuel appears to have been long known, since 

 the researches of archaeologists shew that it was 

 highly probable the Romans, when they occupied 

 Britain, were not unacquainted with its use, coal- 

 cinders having been found as part of the relics of 

 a few Roman stations. Coal was, at all events, 

 known during the Anglo-Saxon period, and 

 employed to some extent as an article of house- 

 hold consumption as early as 852 A.D. In 1259, 

 the first public document respecting this mineral 

 appears. It is in the form of a charter by Henry 

 III. granting liberty to the freemen of Newcastle- 

 on-Tyne to dig for coals. Soon after this, a con- 

 siderable export trade in what was then, and long 

 after, called ' sea-coal' was established with Lon- 

 don ; but, as has been the case with many natural 

 products when first introduced, a strong prejudice 

 sprung up against it in the metropolis. The out- 

 cry about the injurious influence of its smoke on 

 public health at length became so general, that, 

 in 1306, Edward I. issued a proclamation forbid- 

 ding its use. Under the pressure of a decreasing 

 supply of wood, however, its use in London was 

 in a few years resumed. In Scotland, coal was 

 worked in Fife and the Lothians as early as the 

 fifteenth century, and in Ireland not later than 

 the beginning of the sixteenth. From the time of 

 Elizabeth, the coal-trade has been regarded as 

 one of national importance, and since then has 

 continued to flourish, although in the time of 

 Charles I. it was heavily burdened with taxation. 

 In all the large towns of the United Kingdom, coal 

 has been burned since towards the middle of the 

 seventeenth century ; and before the close of the 

 last century, the extension of canals in the Eng- 

 lish manufacturing counties greatly increased its 

 consumption there ; but until the great extension 

 of the railway system in 1845-50, large districts 

 were practically unable to get it on account of the 

 cost of conveyance. The introduction of Watt's 

 steam-engine, however, in 1769, and more espe- 

 cially the rapid extension of its use in manufac- 

 tures and navigation, during the present century, 

 has contributed more than anything else to in- 

 crease the demand for coal, and has, moreover, 

 enabled the miner to supply that demand, by the 

 new facilities it afforded him for raising this fuel 

 from great depths and over extensive areas. Since 

 the introduction of gas-lighting, too, in 1810, a 

 very considerable quantity of coal has been con- 

 sumed at home, as well as exported to other 



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