OF CENTRAL CANADA PART I. 



diamond, carbonate of lead, &c.; the vitreous or glassy lustre- 

 example : rock crystal; the resinous lustre ex.: native sulphur; the 

 pearly lustre ex.: talc; the silky lustre (usually accompanying a 

 fibrous structure) ex.; fibrous gypsum ; the stony aspect; the earthy 

 aspect, &c. These terms sufficiently explain themselves. Occasionally, 

 two kinds of non-metallic lustre are simultaneously present -either 

 blended, as seen in obsidian, which exhibits a " resino- vitreous " 

 aspect ; or distinct as regards different crystal faces or external and 

 internal surfaces. Many of the so-called Zeolites, for example, pre- 

 sent a pearly lustre on the surfaces produced by cleavage (see beyond), 

 whilst the external lustre is vitreous. In Apophyllite, the basal 

 or terminal crystal-plane is pearly, the others vitreous. Micas, and 

 some few other minerals, present a pseudo-metallic lustre. This may 

 be distinguished from the metallic lustre properly so-called, by being 

 accompanied by a degree of translucency, or by the powder of the 

 mineral being white or faintly coloured : minerals of a true metallic 

 aspect being always opaque, whilst their powder is either black or 

 dictinctly coloured. Very few minerals exhibit (in their different 

 varieties) more than one general kind of lustre : metallic or non- 

 metallic. Thus, galena (the common ore of lead), copper pyrites, &c., 

 always present a metallic lustre ; whilst, on the other hand, quartz, 

 feldspar, calc-spar, gypsum, &c., are never metallic in aspect. ' Hence, 

 by means of this easily-recognized character, we may divide all 

 minerals into two broad groups ; and thus, if we pick up a specimen, 

 and wish to ascertain its name, we need only look for it among the 

 minerals of that group with which it agrees in lustre. The first step 

 towards the determinataion of the substance will in this way be 

 effected. 



The degree of lustre may be either splendent, shining, glistening, 

 glimmering or dull ; but the character is one of comparatively little 

 importance. 



Colour. When combined with a metallic aspect, colour becomes a 

 definite character, and is thus of much value in the determination of 

 minerals. As regards a substance of metallic aspect, for example, 

 specimens brought from different localities, or occurring under 

 different conditions, rarely vary in colour beyond a slight difference 

 of depth or shade. Thus, galena the common ore of lead is always 

 lead-gray; copper pyrites, always brass-yellow; native gold, always 



