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NEW ZEALAND NATURE-STUDY BOOK 
mineral shewn and to its crystalline or non-crystalline 
character. Such distinctions, moreover, as those 
which are made between the terms crystalline and 
crystallised should not as a rule be attempted. 
The particular forms of the crystals might be noted, 
but only when the more obvious forms are under 
review, é.g., good specimens of Quartz, Galena or Calcite. 
To attempt anything approaching a systematic study 
of crystallography in these lessons would mean, amongst 
other things, the employment of a terminology which 
could result only in confusion. 
CLEAVAGE.—The tendency to split along definite 
planes possessed by many crystals. Here again the 
amount of attention directed to this property will 
depend largely, if not entirely, on the specimens 
under review. The fact that some minerals split in 
certain definite directions leaving clean even faces, 
whilst others fracture with an uneven surface, will be 
quite enough to attempt. 
SPECIFIC GRAVITY, or the weight of the substance 
compared with that of an equal bulk of distilled 
water at 60° Fahr. or 4° Cent. 
Chemical properties. The investigation of the 
chemical properties of minerals might be confined to: 
A, 
FUSIBILITY, or the property of melting. To melt a 
mineral substance a very hot flame will be required— 
so that this test can seldom be applied. 
INFLAMMABILITY, or the property of uniting rapidly 
with oxygen and so burning. 
BEHAVIOUR on the application of some acid, usually 
Hydrochloric Acid. Carbonates, when treated in this 
way, effervesce owing to the liberation of Carbon-di- 
oxide. 
