May 1, 1864.] THE TECHNOLOGIST. 



ON GRANITE AND ITS USES. 443 



most abundant and common earthy or mineral matter, which, as form- 

 ing the smooth milk-white pebbles of our Highland brooks, Ave dis- 

 tinguish in our vernacular by the contemptuous name of chucky- 

 stones (stones to be chucked about) ; which, as forming the sand upon 

 our sea shores, we count the very type of useless barrenness ; and of 

 which, in its shape of sandstone, we build our rudest walls and meanest 

 erections. 



The whole of the precious stones in question are, in truth, only 

 coloured sandstones. Nor is there anything rare in the source of their 

 colour. A little iron rust, a little manganese, a little coaly matter, or a 

 few scales of mica, are sufficient to give them their beautiful tints. And 

 the most beautiful, perhaps, of all the siliceous gems, the precious opal 

 (of which there exists a piece at Vienna, weighing 1 lb., valued at 

 40,000?.), if it owe its splendid blaze of colours to anything but its 

 structure, owes it only to the presence of a little water. 



Of tbe other eight stones, three — the ruby, the carbuncle, and the 

 sapphire — are identical. The ruby and the carbuncle are exactly so, and 

 the sapphire differs only in colour from them, A ruby or carbuncle 

 may be called a red sapphire or a sapphire may be called a blue ruby. 

 They consist of the same thing as the emery powder with which we 

 clean rusty needles, and it is the same thing as the earth of clay, alumina. 

 The rarest azure-blue sapphire, or blazing ruby, is only crystallised 

 coloured clay-earth. 



Of the remaining five stones, two — the emerald and the beryl — are but 

 different names for one thing. They are largely made up of flint-earth 

 (silica), and clay-earth (alumina), and their colour is owing to an 

 abundant metal, chromium. They do contain, however, one compara- 

 tively rare body called glucina, the oxide of an unfamiliar metal. Yet 

 there is nothing remarkable in the appearance of this body, which is a 

 white powder resembling closely flint-earth and clay-earth, and only 

 occasionally found forming a gem. For it is oidy a few among the 

 beryls that are sufficiently beautiful to be counted among precious 

 stones, and fine emeralds are so rare that a single one (no doubt a large 

 one) at Vienna is valued at 50,000Z. 



The last three stones are the chrysolite, the topaz, and the jacinth. 

 The chrysolite is made up largely of the continually recurring flint- 

 earth, silica ; its rather unattractive yellowish or olive-green colour 

 results from the presence of a little iron rust ; and what is not siliceous 

 or ferruginous in it is the uncostly substance magnesia. The topaz is, 

 again, clay-earth and flint-earth, with the addition of a common body, 

 fluorine. 



At length, however, in the last of the sacred gems, we encounter 

 one constituted of very rare materials. The jacinth is composed of the 

 least common materials of all the gems. It has in it an earth called 

 zirconia, the oxide of a metal which occurs very sparingly in any part of 

 the crust of the globe. This forms two-thirds of it, the other third is 



