CRYSTALS THE MOST BEAUTIFUL
OF MINERAL FORMS
There are three general classes of crystals—calcareous, silicious and gypsum—but by far the most important are the silicious crystals because of their great hardness. These include quartz or rock crystal—which is quite common—and the so-called precious stones, among which are the diamond, rubies, sapphires, etc., a description of which will be found in the [Dictionary of Minerals].
To find the relative hardness of substances, a scale has been arranged, beginning with the softest mineral (talc) and ending with the hardest (diamond). The minerals of the scale, therefore, are so arranged that each will scratch any other mineral of lower number in the scale, or be scratched by any of higher number.
Scale of Hardness
| Mineral | Chemical Name | |||||||
|---|---|---|---|---|---|---|---|---|
| 1. | Talc. | - | Can be scratched by the finger-nail | - | 1. | Magnesium silicate. | ||
| 2. | Gypsum (or rocksalt). | 2. | Calcium sulphate or Sodium chloride. | |||||
| 3. | Calc-spar. | - | Can be scratched by knife or file | - | 3. | Calcium carbonate. | ||
| 4. | Fluor-spar. | 4. | Calcium fluoride. | |||||
| 5. | Apatite. | 5. | Calcium phosphate. | |||||
| 6. | Felspar. | 6. | Potassium and aluminum silicates. | |||||
| 7. | Quartz (rock-crystal). | - | Cannot be scratched by knife or file | - | 7. | Silica. | ||
| 8. | Topaz. | 8. | Aluminum fluosilicate. | |||||
| 9. | Corundum (sapphire, ruby). | 9. | These gems are crystallized alumina. | |||||
| 10. | Diamond. | 10. | Crystallized carbon. | |||||
As a first inquiry into the chemical composition of a mineral, dilute hydrochloric or sulphuric acid is tried. All carbonates effervesce when placed in acid or when acid is dropped upon them, while quartz and all the silicates show no effervescense when so treated.
The table on [pages 104-7] contains a brief description of the distinctive physical features of a number of the very common or important minerals.
DICTIONARY OF IMPORTANT MINERAL PRODUCTS
Aluminum, a metal which does not occur in nature in the free state, but for the most part in combination with silica, as a silicate of aluminum, in clay and many minerals. As extracted from clay by a series of very difficult chemical operations, it forms a white metal, very ductile and malleable, and susceptible of a high polish. On account of its lightness, aluminum is highly valued; it forms excellent alloys.
Bauxite (aluminum hydrate) is the only ore. It is mined in France, Ireland, Austria, Arkansas, Alabama and Georgia, and is refined by electric processes. It is used largely as an addition to iron and steel, preventing bubbles and waste in castings; in electrical work, and for purposes where a light, strong metal is necessary, as in certain machinery, hulls for small boats, etc. Refineries are located in Switzerland, France, Great Britain and United States.