202 



SCIENCE-GOSSIP. 



ARTIFICIAL PRECIOUS STOXES. 



Bv \V. Erkest Ord, B.A. 



'X*'HE marvellous beauty of precious stones has 

 appealed to mankind in all ages. In the 

 East, where they are regarded with a superstitious 

 veneration, the desire to possess them is almost 

 a passion, and if with us this veneration has been 

 diminished owing to more moderate ^•iews concern- 

 ing their virtues, much of their original prestige 

 clings to them. Few people, indeed, can regard, 

 vdthout being thrilled with admiration, a collection 

 of beautiful gems, as they sparkle in the light and 

 dazzle the e3-es by a multitude of reflections. 

 Nature, however, whilst exciting our admiration 

 for these exquisite products of her skill, has 

 granted them only in rare quantities to mankind, 

 and the appreciation for them has been further 

 increased owing to the mystery of their origin, and 

 the impossibility, until recent years, of producing 

 them artificially. With the progress of science it 

 was ine\-itable that mankind could not rest content 

 \',nthout inquiring into the composition and method 

 of formation of these valuable treasures. Their 

 rarity in nature has suggested the value of any 

 method by which their artificial production might 

 be successfully accomplished, and the investiga- 

 tions, so stimulated, have led to the discovery of 

 certain methods by which many of the well-known 

 precious stones can be produced in the laboratory 

 of the chemist. 



Success in the artificial formation of any natural 

 substance is usually attained only when its consti- 

 tution is well understood. Until its analysis into 

 the elementary bodies composing it has been 

 accomplished, and its constitution and properties 

 thoroughl}' studied, no clue can be obtained as to 

 the method by which it may be formed from more 

 common materials. The natural history of precious 

 stones, however, so far as known, does not afi"ord 

 much light as to their actual formation in nature. 

 Their origin is, to some extent, shrouded in mystery. 

 They are usually crystals, supposed to have been 

 formed in rocks by a long process of cooling from 

 a state of verj' high temperature, and they are 

 generallj' found associated with such rocks as a 

 " matrix," or else in the alluvial soil worn down 

 from these rocks into the beds of rivers. The 

 diamond, for example, occurs in a matrix of a 

 kind of sandy freestone, though it is doubtful 

 whether it has ever been found in the place where 

 it was originally formed. The garnet occurs in 

 granite and mica slate, and the ruby in the sands 

 of rivers in Ceylon and in the famous ruby mines 

 of Burmah. 



The study of the chemical constitution and 

 properties of precious stones is instructive and 



indicates the nature of the problem of their arti- 

 ficial production. Thej' are found to be crystalline 

 compounds, more or less complex, of familiar 

 elementary bodies. The diamond, as is well 

 known, is simply pure carbon crystallised. It is 

 most valuable when perfecth' colourless, and is 

 then said to be of the purest water. It may, 

 however, be blue, green, pink, yellow, or black. 

 It is the hardest of gems, and is remarkable for its 

 wonderful limpidity and high refractive power. 

 Though permanent in its form, and unaltered 

 under many varied conditions, it will burn in air 

 at a high temperature, forming carbonic acid 

 gas, the product of the combustion of carbon, 

 whether as diamonds or in the coal of our fires. 

 Man}' of the most valuable gems, again, are formed 

 from the admixture of various substances with 

 alumina. Alumina is the oxide of aluminium, the 

 light metal now much in use, and it is the chief 

 constituent of clay ; but in the crystalline form, 

 and when coloured by traces of other elements, 

 such as chromium, it gives us rubies, sapphires and 

 many other gems. Its combination \\-ith magnesia 

 forms the spinels which are used for the jewelling 

 of watches, and mth glucina it forms the chryso- 

 beryl. The emerald is found to be a compound of 

 alumina, silica and glucina, coloured green by 

 chromium, while the topaz, turquoise, garnet and 

 berjd are all composed of alumina in combination 

 with other substances. Silica, a form of which is 

 the common sand of the sea-shore, when crystalline 

 and coloured by minute traces of iron and man- 

 ganese gives the beautiful amethyst, a transparent 

 stone of a purple or \-iolet colour. In combination 

 with water, again, it forms the opal, which, owing 

 to the diffraction of light its surface produces, 

 exhibits a rich play of prismatic colours. The 

 chalcedony, on3-x and jasper are other stones of 

 which silica is the chief constituent. To a different 

 class of natural substances belongs the pearl, 

 which is found in certain molluscs. It consists of 

 concretions of carbonate of lime, formed in delicate 

 layers around a foreign body, such as a grain of 

 sand, which has found its way into the body of the 

 animal, and against the irritation which it would 

 occasion some protection is desirable. The pearl 

 is found in different colours — white, yellow, pink 

 and black. It is thus seen that these treasures, 

 which appeal so strongly to the admiration of 

 mankind, are composed of ordinary materials, but 

 fashioned by nature's wonderful architecture in 

 the most exquisite forms. 



When we now turn to man's efforts to imitate 

 these beautiful products of nature, we find that a 



