es of the predominant minerals in the ore. Ores
are a mixture of many minerals; the proportions vary through the
same ore-body. Despite this, a few partial analyses, which are
usually available from assays of samples and metallurgical tests,
and a general inspection as to the compactness of the ore, give a
fairly reliable basis for approximation, especially if a reasonable
discount be allowed for safety. In such discount must be reflected
regard for the porosity of the ore, and the margin of safety necessary
may vary from 10 to 25%. If the ore is of unusual character, as
in leached deposits, as said before, resort must be had to the
second method.

The following table of the weights per cubic foot and the number
of cubic feet per ton of some of the principal ore-forming minerals
and gangue rocks will be useful for approximating the weight of
a cubic foot of ore by the third method. Weights are in pounds
avoirdupois, and two thousand pounds are reckoned to the ton.

============================================
| | Number of
| Weight per | Cubic Feet
| Cubic Foot | per Ton of
| | 2000 lb.
------------------|------------|------------
Antimony | 417.50 | 4.79
Sulphide | 285.00 | 7.01
Arsenical Pyrites | 371.87 | 5.37
Barium Sulphate | 278.12 | 7.19
Calcium: | |
Fluorite | 198.75 | 10.06
Gypsum | 145.62 | 13.73
Calcite | 169.37 | 11.80
Copper | 552.50 | 3.62
Calcopyrite | 262.50 | 7.61
Bornite | 321.87 | 6.21
Malachite | 247.50 | 8.04
Azurite | 237.50 | 8.42
Chrysocolla | 132.50 | 15.09
Iron (Cast) | 450.00 | 4.44
Magnetite | 315.62 | 6.33
Hematite | 306.25 | 6.53
Limonite | 237.50 | 8.42
Pyrite | 312.50 | 6.40
Carbonate | 240.62 | 8.31
Lead | 710.62 | 2.81
Galena | 468.75 | 4.27
Carbonate | 406.87 | 4.81
Manganese Oxide | 268.75 | 6.18
Rhodonite | 221.25 | 9.04
Magnesite | 187.50 | 10.66
Dolomite | 178.12 | 11.23
Quartz | 165.62 | 12.07
Quicksilver | 849.75 | 2.35
Cinnabar |