262 NEW ZEALAND NATURE-STUDY BOOK 
Chemical Properties.—If there is a fire in the room, 
put a piece of Coal on and let the class describe exact] 
what takes place. The behaviour of the Coal will differ in 
detail with different varieties, but in all cases it wil] burn 
and not melt, from which we learn that it is inflammable 
and infusible. 
To recapitulate: We have investigated the physical pro- 
perties of the mineral under the following heads :— 
General shape of specimen Cleavage 
Colour Taste 
Lustre Odour 
Power of transmitting light Form (whether crystalline 
(opaqueness or transpar- or non-crystalline) 
ency) Specific gravity 
Brittleness Inflammability 
Hardness Infusibility 
Fracture | 
It will be seen, on referring to Chapter I, that the 
investigation has touched on almost all the headings under 
which the physical and chemical properties of minerals may 
be considered. Some such method should in every case 
be adopted, in order that, as the subject progresses, 
comparisons and contrasts may the more readily be made. 
Origin.—Though Coal consists of compressed vegetation, 
traces of organic structure can be seen only on careful 
examination. This, however, frequently discloses portions 
of stems, leaves, or carbonised woody fibre in the coal seam 
itself, and impressions of leaves and other parts of plants in 
the rocks casing or enclosing the seam. 
Exposed to atmospheric conditions dead vegetation goes 
to form humus, and so to increase the soil. Withdrawn 
from the atmosphere, however, exposed to the action of 
water, especially with an increase of temperature, and 
under sufficient pressure, dead vegetation is converted into 
