436 SCIENTIFIC RECREATIONS. 



given for diamonds, which, after all, are only carbon in a pure state. Anothet 

 form of carbon is graphite (plumbago, or blacklead). It is much used for 

 pencils and in households. It is found in Cumberland, and in many other 

 localities in Europe and Canada 



Carbon appears in one or other of the above forms in regular octa- 

 hedrons or their allied shapes. Anthracite, another form of carbon, is used 

 as fuel for strong furnaces. It leaves little " ash," and is smokeless when 

 burned. Coal, in all its forms, is evidently derived from wood. Thousands 

 of years ago vegetable matter must have been embedded in the ground and 

 subjected to carbonization. There are different kinds of coal, all of which 

 come under one or other of the following heads : cubical coal, slate coal, 

 cannel coal, glance-lignite, the last being, as its name implies, an imperfect 

 development of wood ; it is a brown coal. We are not here concerned with 

 coal as a fuel. Charcoal is also a form of carbon prepared from wood and 

 finds a counterpart in coke, which is prepared from coal. Carbon, as we have 

 already seen, plays an important part in electric lighting and in the Voltaic 



Fig. 458. Crystals of carbon. 



Battery. Peat, or as it is called in Ireland, " turf," is one of the most recent 

 of the carboniferous formations. It is much used as fuel. It is cut from 

 moors ( u bogs," as they are sometimes called), and the various deposits can 

 be traced. Bog-oak is no doubt the first step towards peat, as peat is the 

 step towards coal. The brown turf is newer than the black, and both kinds 

 may be seen stacked in small square " bricks " along the Irish canals and in 

 the yards of retailers of fuel. 



SILICON. Silica occurs generally in combination with alumina, and 

 never in a free state. In combination with oxygen it is called silicic acid. 

 Silica, when crystallized, is usually called quarts. 



QUARTZ has several varieties. We need only enumerate them, they 

 will all be immediately recognized. We give illustrations of the crystals of 

 quartz (fig. 459): ' 



1. Rock crystal appears in beautiful six-sided prisms 



2. Amethyst is coloured by protoxide of manganese, supposed by the ancients to be a 

 charm against drunkenness. 



3. Common quartz, or quartz rock, forms granite in combination, and is also known as 

 "cat's-eye," " rose" quartz, etc. 



