CHAPTER II.
DIRECTIONS FOR DETERMINING SPECIMENS BY THE KEY.
HOW TO TEST MINERALS WITH THE SIMPLEST MEANS—PROSPECTING WITH A JACK-KNIFE AND COMMON SENSE—USE OF THE KEY—HOW TO TELL PYRITES FROM GOLD AND QUARTZ FROM DIAMOND—ALL THE USEFUL MINERALS GROUPED ACCORDING TO HARDNESS AND COLOR.
FIRST see whether it will scratch common window-glass. If it will make the least mark, it belongs to division A; if not, it is to be found in group B. Next notice whether the light will shine through it: if it does not pass through even the edges or a thin splinter, it is opaque; if any light is allowed to pass, it is translucent. With a knife see if it is harder or softer than pure white marble; then, noting its color, compare it with the descriptions of minerals referred to by the numbers. If it agree with none, it may be considered of no use in the arts. To make doubly sure, get the gravity as described on page 12.
Examples: Suppose we have an unknown mineral in hand. We first try to scratch glass with it and find it impossible. It therefore belongs to section B. Next we find it is opaque and yellow, and evidently heavier and harder than marble. It must be one of two: 44 attracts the compass-needle, and this will not; it is consequently 26 or Copper Pyrites, if it agree with the description. If not, it is something of no great value.
You have found what you think is a diamond, Does the specimen scratch glass? Yes, easily, and is brittle. Can you see through it? You say it is clear as glass. Look now under section A, “translucent” series, number 6 (for it is colorless), and decide which of the four it is. The first one (27), is diamond; but do not let your wishes make it agree. Turning to the description, you read that it can not be scratched with a file or worn down on a grindstone. This decides against it. Besides, the gravity (2.5) is too little. With the next (57) it agrees perfectly, and you need not go further. Should the specimen, however, agree very well with rock crystal, only that its gravity (3.5) is too great, then it is topaz.
☞ All minerals that scratch glass are brittle, and all (save 32 and 46) are infusible or melt with great difficulty.
☞ The following minerals will burn, evaporate or melt without a flux in an ordinary fire: Nos. 2, 4, 5, 7, 10, 13, 14, 16, 18, 19, 21, 23, 24, 26, 29, 33, 35, 37, 44, 53, 55, 62, 63, 70, 71, 75. All but the following are heavier than marble: 2, 4, 6, 7, 10, 14, 16, 34, 36, 40, 47, 48, 56, 60, 61, 69, 71. Nos. 2, 50 and 58 alone dissolve in water.
☞ In determining color, be sure you have a fresh surface, for the outside is often deceptive. By “blow-pipe” is meant the tapering tube used by watch-makers.
A.
WILL SCRATCH GLASS.