210 BULLETIN 118, UNITED STATES NATIONAL MUSEUM. 



II. Color violet, red-violet, and related hues. 



A. Transparent or nearly so. 



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



1. Does not scratch corundum surface Corundum (oriental amethyst). 



(The rare violet-colored diamond belongs here; it scratches corundum.) 

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



1. Specific gravity very high, 4 Garnet (almandine and rhodolite). 



2. Specific gravity high, 3.6 Spinel. 



3. Specific gravity rather high, 3.2 Spodumene (kunzite). 



4. Specific gravity medium, 2.65 Quartz, amethyst. 



(The rare violet-colored varieties of iolite, tourmaline, and zircon, and 

 the rare mineral axinite, belong here.) 

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



1. Isotropic Glass (artificial). 



(The rarely used violet varieties of apatite belong here.) 



B. Opaque or nearly so. 



(a) Hardness greater than 6; scratch microcline. 



(The rare violet chalcedony and the rare mineral dumortierite belong here.) 

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



(The rarely used lepidolite, pyroxene variety violan, and opaque violet 

 glass belong here.) 



III. Color blue and related hues. 



A. Transparent or nearly so. 



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



1. Does not scratch corundum surface Corundum, sapphire. 



(The rare blue-colored diamond belongs here; it scratches corundum.) 

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



1. Sp.gr. 4.6; color pale blue, essential Zircon. 



2. Sp. gr. 3. 6; color deep green-blue, essential Spinel. 



3. Sp.gr. 3.5; color pale blue, disperse Topaz. 



4. Sp. gr. 3.1 ; color deep smoky or green-blue, essential .Tourmaline (indicolite). 



5. Sp. gr. 2.7; color pale blue or green-blue, disperse Beryl, aquamarine. 



6. Sp. gr. 2.6; pleochroic, blue to yellow Iolite. 



(The rare mineral euclase belongs here.) 

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



1. Isotropic Glass. 



(The rare blue-colored varieties of apatite, fluorite, kyanite, and opal, and 

 the rare minerals benitoite and hauynite, belong here.) 



B. Opaque or nearly so. 



(a) Hardness greater than 6; scratch microcline. 



1. Luster waxy (in part artificially colored by dyes) Chalcedony. 



2. Luster glassy; color due to inclusions Quartz. 



(6) Hardness 6 or less; do not scratch microcline. 



1. Sp. gr. 3.8; color deep blue; effervesces with acid . . . Azurite. 



2. Sp. gr. 2.8; color pale green-blue; luster waxy Turquois. 



3. Sp. gr. 2.4; color mottled and showing pyrite dots Lapis-lazuli. 



(Several little-used minerals belong here, such as calamine (copper- 

 stained), chrysocolla, crocidolite, smithsonite (copper-stained), sodalite, etc.; 

 also glass imitations of turquois.) 



IV. Color green. 



A. Transparent or nearly so. 



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



1. Does not scratch corundum surface Corundum, oriental emerald. 



(The rare green-colored diamond belongs here; it scratches corundum.) 



