Apatite suffered in demand when the cheap phosphates of South Carolina were discovered, and these in turn are being ousted from the markets of the world by Thomas slag, an artificial phosphate, and by the easily-mined natural phosphates of Algeria. The price varies with the quality of the rock, from $1.75 to $11 per ton, averaging in 1899, $3.86.
Apatite is a phosphate of lime, containing 43 per cent. of phosphoric acid. It occurs in the old crystalline and primary rocks of Canada, but although still of some value it has yielded the position it once occupied to the Carolina phosphate deposits, which, although not so rich in acid, are softer, and less expensive to utilize. Apatite is doubtless derived from the remains of animals or fishes that lived in the distant past. The colors are often beautiful—green, pink, gray, etc.—but the sheen is always white. Hardness of 4.8. Specific gravity, 3.1.
Asbestos. This fibrous silicate of magnesia and lime is to be looked for among primary rocks near serpentine dike. The fibers of this material may be woven into cloth that will be fire-proof. It is of considerable, though fluctuating, value.
The demand for this material is likely to increase, though at present the supply is fully equal to demand. It is being used in Germany to make fire-proof paper, and in Quebec to make asbestos plaster for covering wood-work. It is generally quarried in open pits, the rock being crushed in a rock-breaker, and the fiber freed from adhering particles of rock and dust. It is then sorted, the longest fibers going into the first quality heap. The production in 1899 in the United States was 912 tons, value $13,860; in Canada, 23,266 tons, value $598,736.
Borax. This mineral is borate of soda. Its composition is: 37 per cent. boric acid, 16 per cent. soda, and 47 per cent. water. Its gravity is 1.7. Hardness, 2.3. It is white, and has a sweetish taste. Borax is valuable, but occurring as it does as an incrustation upon the ground over large areas, a detailed description would be superfluous, as the explorer will surely recognize it should he find it.
Clay. A good bed of clay may be of value in an accessible region. Brick-clay contains silica, alumina, iron, etc. Potters' clay is made by suspending ordinary brick-clay in water, and running off the water and fine particles suspended therein. These are allowed to settle, and, when dry, are fine potters' clay. The better the clay, the larger the percentage of potters' clay. Fire-clay should contain 60 per cent. of silica, and 30 per cent. of alumina. Mixed with sand and burnt into bricks, it will resist great heat. Light-colored clays are preferable for this purpose, as iron is prejudicial to a good fire-brick. Kaolin is the finest porcelain clay, and the best comes from China, Japan or France. It is a product of decay in feldspar rocks. The potash is washed out, and the silica and alumina left as parts of a white clay of fine grain.
Coal. Anthracite is bituminous coal that has been subjected to great heat and pressure; in plain language, baked. It contains over 90 per cent. of carbon. Specific gravity 1.5 to 1.8. Hardness, 2.3 to 2.6. The ash left after burning is white or red. There is little or no sulphur in anthracite. It does not coke.
There are three main divisions of coal, arranged according to their carbon, water and ash. They are:
| Carbon. | Water. | Ash. | |
| Anthracite | 80-95 p.c. | 2-3 p.c. | 4-10 p.c. |
| Bituminous | 45-80 p.c. | 1-5 p.c. | 8-20 p.c. |
| Lignite | 7-45 p.c. | 15-36 p.c. | 6-40 p.c. |
Good bituminous coal contains about 85 per cent. of carbon, but the composition varies greatly. Cannel coal is a variety of bituminous that gives off much gas. It burns with a bright flame in an open grate, igniting as easily as a candle. Lignite is intermediate between coal and peat. All the Rocky Mountain coals are lignites. It is a very inferior coal at its worst, while at its best it is nearly the equal of a poor bituminous coal.