GEMS OP AUSTEALIA. 77 



2. By submitting tlie mineral to heat witli the blow-pipe, or, 

 in some cases, the flame of a candle, or jet of gas ; as some 

 minerals impart a colour to the flame, or give off" fumes of sulphur, 

 or garlic, &c., or water ; or melt more or less readily with, and 

 without a flux : e.g. native bismuth, sulphuret of antimony, and 

 sulphuret of silver, &c., are easily reduced to the fluid state in 

 the flame of a candle, &c. The operator must carefully note the 

 comportment, or behaviour of the mineral substance under exami- 

 nation ; and any work on mineralogy will point out the character- 

 istics of each mineral before the blow-pipe. 



3. By colour. — This is a most useful test in the case of gems, 

 when once the eye has become accustomed to discriminate the 

 various tints assumed by the several species of gems ; for instance, 

 the almandine garnet (often called a carbuncle, when cut by the 

 lapidary en caboclwn, i.e., with a rounded top) has a red-purple 

 colour, like claret ; the precious garnet has a red or red-brown 

 colour, like port wine (these varieties being valuable as gems) ; 

 and the common garnet has the brown tint predominating ; whilst 

 the opaque garnet is of a black-brown tint (both varieties being 

 unfit for jewellery) . Every connoisseur knows how much the value 

 of the ruby depends on its having the true " pigeon's-blood" 

 colour ; the blue sapphire a deep rich blue ; and the diamond the 

 purity of a drop of distilled water. 



4. By hardness. — This is one of the most unerring tests in the 

 hands of an experienced observer, and the requisite skill is not 

 difficult of acquisition ; but as it is necessarily dependent on 

 comparison, — one mineral with another, — an acknowledged scale of 

 degrees of hardness, which could be adopted by all mineralogists, 

 was a great desideratum. Professor Mohs, the eminent mineralo- 

 gist, accordingly proposed the following Scale ; which has been 

 since universally accepted by mineralogists, for the purpose of 

 expressing the relative hardness of any given mineral. 



It will be seen that the diamond is the hardest mineral, as it is 

 the hardest substance, in Nature. And it may not be deemed out 

 of place to notice a vulgar error which has caused the destruc- 

 tion of many a veritable diamond, owing to persons confounding 

 the terms "hardness" with toughness. Now, the diamond, though 

 so intensely hard, has so little toughness in its nature that with 

 a blow of the smallest hammer you may cleave off" a slice ; and 

 the knowledge of this property enables the diamond-cutter to 

 reduce it a good deal by " cleavage" to the desired form, without too 

 much waste in grinding ; whilst, on the other hand, it constantly 

 happens that a careless workman, in the act of resetting a dia- 

 mond in a piece of jewellery, breaks a splinter off, by allowing the 

 tool to bear too roughly, or smartly upon the gem. And yet there 

 is a common belief among illiterate people, that a diamond is so 

 tough, as well as hard, that " it can hear the lloiv of a sledge- 



