. 201. OPTICAL PROPERTIES OF MINERALS. 287 



Ex. llhonibohedral Corundum (the bright coloured varieties 

 of Sapphire); prismatic Disthene-spar ; and hexahedral 

 Rock-salt. 



7. Smalt-blue. The colour of a pale coloured sort of 

 smalt, called Eschcl. Ex. Several varieties of prismatoidal 

 Gypsum-haloide. 



8. Indigo-blue. Blue mixed with black and gi'een. The 

 colour of several coarser sorts of indigo. Ex. Prismatic 

 Iron-mica, particularly the decomposed or imperfectly form- 

 ed varieties called Blue Iron-earth. 



9. Duck-blue. Blue, with a great deal of green, and a 

 little black. Ex. Several varieties of dodecahedral Corun- 

 dum, called Ceylanite ; also several varieties of prismatic 

 Talc-mica, under the denomination of common Talc. 



10. Sky-blue. A pale blue colour, with a little green. 

 It is called Mountain blue by painters ; it is the colour of 

 the clear sky. Ex. Prismatic Larocone-malachite, some- 

 times also octahedral Fluor-haloide. 



E. Green. 



1. Verdigris-green. A green colour, very much inclining 

 to blwe. It is the colour of verdigris (Acetite of Copper), 

 Ex. Amazon-stone, which is a variety of prismatic Feld- 

 spar, and prismatic Lirocone-malachite. 



2. Celandine-green. A green colour, mixed with blue 

 and grey. Ex. Prismatic Talc-mica, called Green-earth ; 

 several varieties of rhombohedral Emerald. 



3. Mountain-green. Green, with a great proportion of 

 blue. Ex. Rhombohedral Emerald ; prismatic Topaz, the 

 oriental Aqua-marine. 



4. Leek-green. Green, with a little brown ; the colour 

 of the leaves of garlick. Very distinct in rhombohedral 

 Quartz, called Prasem. 



5. Emerald-green. The purest green colour. Very dis- 

 tinct in rhombohedral Emerald ; less characteristic in some 

 varieties of hemi-prismatic Habroneme-malachite. 



6. Apple-green. A light green colour, with a trace of yellow. 

 Very distinct in rhombohedral Quartz, called Chrysoprase. 



