4 A POPULAR EXPOSITION OF THE 
and wish to ascertain its name, we need only look for it amongst the 
minerals of that group with which it agrees in lustre. The first step 
towards the determination of the substance will in this way be ef- 
fected. 
The degree of lustre may be either splendent, shining, glistening, 
glimmering, or dull; but the character is one of comparatively little 
importance. 
2. Colowr.—When combined with a metallic aspect, colour becomes 
a valuable character in the determination of minerals, because it then 
_remains constant as regards a given substance. Thus galena, the 
common ore of lead, is always lead-grey; copper pyrites, always 
brass-yellow; native gold, always gold-yeilow; and so forth. When 
accompanied, however, by a vitreous or other non-metallic lustre, 
colour is, practically, a character of no value; as in that case, the 
mineral may present, in its different varieties, every variety of colour. 
Thus, we have colourless quartz, amethystine or violet quartz, red 
quartz, yellow quartz, &c., just as in the vegetable kingdom, we have 
red, white, and yellow roses; and dahlias, &c., of almost every shade. 
When combined with a metallic aspect, the colour is said to be me- 
tallic ; and of metallic colours we may enumerate the following : 
White Silver-white ...... ex. Native silver. 
Dea whiten... ce. ex. Pure tin; cobalt ore. 
Grey «. Lead-grey......... ex. Galena. 
‘ Steel-grey......... ex. Specular iron ore. 
Black ......Ivon-black (usually with sub-metallic lustre) ex. Mag- 
netic iron ore. 
Gold-yellow ...... ex. Native gold. 
Yellow.. Brass-yellow. .... ex. Copper-pyrites. 
«{ Bronze-yellow (a brownish-yellow) ex. Magnetic pyrites. 
edt. oes Copper-red ....... ex. native copper. 
These metallic colours are often more or less obscured by a black, 
brownish, purple, or iridescent surface-tarnish. Hence, in noting the 
colour of a mineral, a newly-fractured surface should be observed. 
The non-metallic colours 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, &e. 
_In minerals of a non-metallic aspect, the colour is sometimes uni- 
form’; and at other times, two or more colours are present together, in 
