Method of Comparing the Hardness of Electric Furnace Products and Natural Abrasives

Abstract

By measuring the relative resistance to abrasion during lapping, it is possible to evaluate the comparative hardness of crystalline minerals and electric furnace abrasives. The method gives results which can be duplicated with a fair degree of accuracy, and, where small variations in hardness exist, these variations can be repeatedly detected over a large number of measurements. Considerable variation in hardness exists among the various types of diamonds. With the tests described, the South American brown bort diamonds were found to be consistently harder than other types, although the South American ballas possessed a hardness which was almost identical with the bort. The carbonado diamond, which is usually considered the hardest of diamonds, was found to be considerably softer than the other varieties. The interval of hardness between corundum and the diamond is much greater than would be realized from a consideration of the Mohs' scale, and a comparative scale has been given, extending from the diamond to quartz.