OPTICAL CHARACTERS OF MINERALS. 105 



The Metallic Lustre, is subdivided into perfect and imperfect, me- 

 tallic lustre. The first of these occurs in the pure metals, their al- 

 loys, and occasionally in their oxides and combinations with sulphur, 

 as in Galena and Iron Pyrites ; the second is found in the oxides 

 of the metals for the most part, and is particularly exemplified in 

 Columbite. 



The Adamantine Lustre, is subdivided into metallic adamantine, 

 and common adamantine. The common adamantine is nearly pe- 

 culiar to the Diamond ; the metallic adamantine is found in Red Sil- 

 ver ore and some varieties of Carbonate of Lead. 



The Resinous Lustre is well understood from our knowledge of 

 it in Resin. It may further be defined as presenting the appearance 

 of a body besmeared with oil or fat. It is best seen in Pitchstone. 



The Vitreous Lustre is that of glass, and may be observed in 

 common Quartz. 



The Pearly Lustreis divided into common and metallic, pearly lus- 

 tre. The first which approaches the nearest that of the pearl, is 

 found in Heulandite, Stilbite, and some varieties of Mica : the se- 

 cond occurs in Bronzite and Hyperslene. 



As to the intensity of lustre, the following degrees are distin- 

 guished : 



1. Splendent, 



2. Shining, 



3. Glistening, 



4. Glimmering, 



5. Dull. 



Splendent, applies to those faces which possess the highest degree 

 of lustre; and which produce distinct and well defined images, of 

 external objects, provided they are of sufficient dimensions and 

 evenness. Such faces are contained in Garnet, Blende, Tin ore, &.c. 



Shining, is the next less degree of lustre ; it does not produce re- 

 flections equally distinct. Calcareous Spar, and Sulphate of Ba- 

 rytes often present examples of it. 



Glistening, is that in which the light is reflected still less 

 distinctly ; but though it does not yield an image, it reflects it in 

 pretty well defined patches. This degree of lustre is found in most 

 of those compound minerals in which the particles of composition 

 are still observable. Examples are Copper Pyrites, and Grey Ox- 

 ide of Copper. 



Glimmering does not reflect defined patches of light, but a mass 

 of undefined light seems spread over the glimmering surface. This 



