108 GENERAL CHARACTERS OF PRECIOUS STONES 



■or more often, according to their value. Frequently they are divided into two main groups, 

 the true precious stones or jewels, and the semi-precious stones. K. E. Kluge, in his 

 Handbuch der JEdelsteinJcunde, published in 1860, distinguishes five groups of precious 

 stones, characterised by their value as gems, their hardness, optical characters, and rarity of 

 occurrence. Other methods of grouping are, of coui'se, equally possible. There are no 

 sharp lines of division between such groups, which are to a certain extent arbitrary, and 

 there are many stones which would be placed by one authority in one group, and by 

 another authority in another group. As an example of a possible method of gi'ouping, the 

 following classification by Kluge, in which the stones are arranged according to their 

 market value, may be given. 



1. True Pkecious Stones or Jewels. 



Distinguishing characters are : great hardness, fine colour, perfect transparency, com- 

 bined with strong lustre (fire), susceptibility of a fine polish, and rarity of occurrence in 

 ■specimens suitable for cutting. 



A. Gems of the First Rank. 



Hardness, between 8 and 10. Consisting of pure carbon, or pure alumina, or with 

 alumina predominating. Fine specimens of very rare occurrence and of the highest value. 



1. Diamond. 



2. Corundum (ruby, sapphire, &c.). 



3. Chrysoberyl. 



4. Spinel. 



B. Gems of the Second Rank. 



Hardness, between 7 and 8 (except precious opal). Specific gi-avity usually over 3. 

 Silica a prominent constituent. In specimens of large size and of fairly frequent occurrence. 

 Value generally less than stones of group A, but perfect specimens are more highly prized 

 than poorer specimens of group A. 



5. Zircon. 



6. Beryl (emerald, &c.). 



7. Topaz. 



8. Tourmaline. 



9. Garnet. 



10. Precious Opal. 



C. Gems of the Third Rank. 



These are intermediate in character, between the true gems and the semi-precious 

 stones. Hardness, between 6 and 7. Specific gravity usually greater than 2'5. With the 

 exception of turquoise, silica is a prominent constituent of all these stones. Value usually 

 not very great ; only fine specimens of a few members of the group (cordierite, chrysolite, 

 turquoise) have any considerable value. Specimens worth cutting of comparatively rare 

 occurrence, others fairly frequent. 



11. Cordierite. 16. Staurolite. 



12. Idocrase. 17. Andalusite. 



13. Chrysolite. 18. Chiastolite. 



14. Axinite. 19. Epidote. 



15. Kyanite. 20. Turquoise. 



2. Semi-Precious Stones. 



These have some or all of the distinguishing characters of precious stones, but to a less 

 marked degree. 



