.200. OPTICAL PROPERTIES OF MINERALS. 283 



WERNER, to whose labours this part of Terminology is 

 particularly indebted. These colours are, White, Grey, 

 Black, Blue, Green, Yellow, Red, and Brown. Each of them 

 comprehends several varieties, of which again the one con- 

 sidered the purest, is called the cliaractcrlstlc colour. The 

 names or denomination of the varieties are either derived 

 from such bodies in which they are found often or by pre- 

 ference, or they are formed by composition. Examples of 

 the first are, rose-red, apple-green, gold-yellow ; of the latter, 

 reddish-brown, yellowish-brown, greyhJi-wlntc, &c. 



The Wernerian method in the determination of colours 

 is as generally introduced and received as it deserves. It 

 is not advisable to change or alter any thing without the 

 most urgent necessity, even though, from other reasons, 

 these alterations should be improvements ; since there is 

 nothing required, but to recal a certain impression upon 

 our mind : and the best plan therefore will be to keep to 

 such expressions to which we have been accustomed. 



. 200. METALLIC COLOURS. 



The metallic colours are: 1. Copper-red; 2. 

 Bronze-yellow; 3. Brass-yellow, and 4. Gold-yel- 

 low ; 5. Silver-white, and 6. Tin-white ; 7. Lead- 

 grey, and 8. Steel-grey, and 9. Iron-Hack. 



1. Copper-red, the colour of metallic copper. Examples, 

 Octahedral Copper ; less distinct prismatic Nickel-pyrites. 



2. Bronze-yellow, the colour of several metallic, alloys 

 called Bronze and Speise, in particular the alloy of copper 

 and tin. Very distinct in hexahedral and prismatic Iron- 

 pyrites. 



3. Brass-yellow, the colour of brass. Ex. Pyramidal Cop- 

 per-pyrites. This colour is never found in hexahedral Gold. 



4. Gold-yellow, the colour of pure gold. Distinct, but 

 exclusively in hexahedral Gold. The gold-yellow colour 

 sometimes becomes pale, and then approaches to silver- 

 white. 



