APPENDIX 6. 

 TABLES FOR THE IDENTIFICATION OF PRECIOUS STONES. 



The accurate identification of a precious stone, even by an expert, 

 is often a matter of considerable difficulty, and, indeed, sometimes 

 rendered quite impossible by the manner in which the stone is 

 mounted. The task, as a rule, is quite beyond the skill of the un- 

 trained. The method given below has been prepared by Dr. Edgar 

 T. Wherry, formerly in charge of the Division of Mineralogy. The 

 appliances needed comprise: 



Sharp-pointed fragments of the minerals diamond, corundum, 

 and quartz, preferably set in wooden handles the size of ordinary 

 lead pencils. 



Cleavage pieces or crystals, with good bright surfaces, of the min- 

 erals corundum, quartz, and feldspar (microcline) . 



Some means for determining specific gravity, such as picnometer, 

 fine platinum-wire cage to be hung on chemical balance, small Nichol- 

 son hydrometer, etc. Liquids with high specific gravities, upon 

 which stones of lower gravity will float, such as methylene iodide, 

 specific gravity 3.30; acetylene tetrabromide, specific gravity 2.95; 

 and bromoform, specific gravity 2.85, are also useful. 



A microscope provided with nicol prisms, and a small, round- 

 bottomed glass dish to be placed in the center of its stage, in which 

 the stone can be immersed in a high-refracting liquid such as 

 ct-mono-brom-naphthalene, n = 1.66. 



The stone is: 



I. Colorless, white, or very pale tinted. 



A. Transparent or nearly so. 



(a) Hardness 9 or greater; not scratched by corundum point. 



1. Scratches corundum surface; not scratched by diamond point Diamond. 



2. Does not scratch corundum surface Corundum (white sapphire). 



(6) Hardness 8 to 7; scratched by corundum, but not by quartz. 



1. Specific gravity very high, 4.5 Zircon. 



2. Specific gravity high, 3.5 Topaz. 



3. Specific gravity medium, 2.65 Quartz (rock crystal). 



(Colorless varieties of beryl, chrysoberyl, garnet, spinel, spodumene, and 

 tourmaline, and the rare minerals danburite and phenakite, belong here.) 

 (c) Hardness les3 than 7; scratched by quartz. 



1. Isotropic between crossed nicols under the microscope Glass (artificial) . 



2. Anisotropic Feldspar (varieties). 



(The rare minerals beryllonite and datolite belong here.) 



B. Opaque or nearly so. 



(a) Hardness greater than 6; scratch microcline. 



1. Luster waxy; not scratched by quartz Chalcedony. 



2. Luster greasy ; scratched by quartz Jade . 



(Compact white vesuvianite (californite) belongs here.) 



(b) Hardness less than 6; do not scratch microcline. 



(White agalmatolite, serpentine, opal, and opaque glass belong here.) 

 4555°— 22 16 209 



