6 MINERALS AND GEOLOGY 



gold-yellow ; and so forth. When accompanied, however, by a 

 vitreous or other non-metallic lustre, colour becomes a character of 

 no practical value, as a mineral of non-metallic aspect may present, in 

 its different varieties, every variety of colour. Thus, we have col- 

 ourless quartz, amethystine or violet quartz, red quartz, yellow quartz, 

 &c. Also, feldspars, fluorspars, and other minerals of variable colour : 

 just as in the Vegetable Kingdom, we have red, white and yellow 

 roses, and dahlias, &c., of almost every hue. The more common shades 

 of metallic colour are as follows. 



w , ., ( Silver-white ex. Native silver. 



' \ Tin- white ex. Pure tin ; cobalt ore. 



p ( Lead-grey ex. Galena. 



' 1 Steel-grey ex. Specular iron ore. 



Black Iron-black (usually with sub-metallic lustre) ex. Magnetic iron ore. 



! Gold-yellow ex. Native gold. 

 Brass-yellow ex. Copper pyrites. 

 Bronze-yellow (a brownish-yellow) ex. Magnetic pyrites. 



Red Copper-red ex. Native copper. 



These metallic colours are often more or less obscured by a black, 

 brownish, purple, or iridescent surface-tarnish. In noting the colour 

 of a mineral, this must be constantly borne in mind, and if possible 

 a newly-fractured surface should be observed. The non-metallic col- 

 ours comprise, white, grey, black, blue, green, red, yellow, and brown, 

 with their various shades and intermixtures : as orange-yellow, straw- 

 yellow, reddish-brown, greenish-black, &c. In minerals of a non- 

 metallic aspect, the colour is sometimes uniform ; and at other times, 

 two or more colours are present together in spots, bands, &c., as in 

 the varieties of quartz called agate, blood-stone, jasper, and so forth- 

 In most varieties of Labradorite, or Labrador Feldspar, a beautiful 

 play or change of colour is observable in certain directions. The finer 

 varieties of Opal also exhibit a beautiful and well known iridescence. 



Streak. Under this technical term is comprised the appearance or 

 colour of the scratch, produced by drawing or " streaking " a mineral 

 across a file or piece of unglazed porcelain. The character is a valuable 

 one on account of its uniformity : as no matter how varied the colour 

 of a mineral may be in different specimens, the streak will remain of 

 one and the same colour throughout. Thus, blue, green, yellow, red, 

 violet, and other specimens of fluor spar, quartz, &c., exhibit equally a 

 white or "uncoloured" streak. The streak is sometimes " unchanged," 



