GEOLOGY. 
69 
for determining minerals generally, and a small blow-pipe case might 
be added to a traveller’s kit, if he thinks it probable that he may 
meet with minerals in any quantity. But in general they are not to be 
found in such profusion as to render it difficult to carry away specimens 
sufficient for determination at leisure. A blow-pipe, too, is of no use to 
any one unacquainted with the method of employing it, though this is 
easy to acquire.* 
To form a rough idea of the value of iron ore, see whether it is heavy; 
to form some notion of the quality of coal, pile up a heap and set fire to 
it. If it does not burn freely, the prospects of the coal being useful are 
small. It may be anthracitic, and very valuable with proper appliances; 
but anthracite is not of the same general utility as bituminous coal. 
Good coal should burn freely, with more or less flame, and should leave 
but little ash, and it is preferable that the ash should be white, not red, 
as the latter colour is often due to the presence of pyrites, a deleterious 
ingredient. 
Gold and gems have, as is well known, been procured in consider¬ 
able quantities from the sands of rivers and alluvial deposits. The 
deposits known to the natives of any country are often of small value, 
and the rude methods of washing prevalent in so many lands suffice 
to afford a fair idea of the wealth or poverty of the sand washed. 
Gold and, wherever it is found, platinum occur in grains and nuggets, 
easily recognised by their colour and by their being malleable; but gems, 
such as diamond, ruby, sapphire, are not so easy to tell from less valu¬ 
able minerals. They may be recognised by their crystalline form and 
hardness. A diamond is usually found in some modification of an octo- 
hedron, and the crystalline facets are often curved; rubies and sap¬ 
phires are really differently coloured varieties of the same mineral, and 
occur, when crystalline, in six-sided pyramids or some modification. A 
diamond is the hardest of known substances; nothing will scratch it, and 
it will scratch all other minerals. Sapphire will scratch everything 
except diamond. 
* There are plenty of good works on the use of the blow-pipe. The best are 
by Plattner and Scheerer, of both of which English translations have been pub¬ 
lished. Of You Kobell’s tables for the determination of minerals, several trans¬ 
lations have appeared. 
