. 196. OPTICAL PKOPEKTIES OF MINERALS. 279 



The kinds of lustre are : 



1, Metallic lustre, 



2, Adamantine lustre, 



3, Resinous lustre, 



4, Vitreous lustre, 



5, Pearly lustre. 



Metallic lustre is subdivided into perfect, and wiper- 

 feet metallic lustre. The first occurs in all the species 

 of the orders Metal, Pyrites, and Glance, and in some of 

 those of the order Ore. The same lustre occurs in wrought 

 metals and metallic alloys, as silver, brass, copper, &c. 

 The second is found in several ores, as Tantalum-ore, 

 Uranium-ore, &c. 



Adamantine lustre is subdivided into metallic adamantine 

 lustre, and common adamantine lustre. Examples of the 

 first may be seen in the dark-coloured varieties of several 

 species of the order Blende, and in some, particularly the 

 grey varieties of di-prismatic Lead-baryte ; the common 

 adamantine lustre is peculiar to octahedral Diamond, to the 

 pale-coloured varieties of Ruby -blende and Garnet-blende, 

 and to some varieties of di-prismatic Lead-baryte. 



Resinous lustre is that which a body presents, if besmeared 

 with oil or fat. It occurs in dodecahedral Garnet, still more 

 distinctly in pyramidal Garnet ; also in the varieties of 

 empyrodox Quartz, called Pitchstone. 



Vitreous lustre is that of common glass, and may be ob- 

 served in rhombohedral Quartz, rhombohedral Emerald, 

 prismatic Chrysolite, and in several other species of the 

 order Gem. 



Pearly lustre is divided into common, and metallic pearly 

 lustre. The first occurs in prismatoidal and hemi-pris- 

 matic Kouphone-spar, in prismatic Disthene-spar, in rhom- 

 bohedral Talc-mica, and in other species of the order 

 Mica ; the second is found in several species of Schiller- 

 spar, and in several varieties of rhombohedral Talc-mica. 



As to the intensity of lustre, we have to distinguish the 

 following degrees : 



