Volume 1

Outlines of mineralogy, geology, and mineral analysis / By Thomas Thomson.

  • Thomson, Thomas, 1773-1852.
Date:
1836
Catalogue details

Licence: Public Domain Mark

Credit: Outlines of mineralogy, geology, and mineral analysis / By Thomas Thomson. Source: Wellcome Collection.

    26/752 (page 10)
    We must carefully distinguish between toughness and hard- ness. By the former is meant difficult frangibility, or a resistance which the particles offer to be separated from each other. By hardness, is meant the property which one mineral has of scratching another, or the power which it has to resist the action of the file. When a mineral is capable of scratch- ing another, we consider it as the harder of the two. Thus, quartz is capable of scratching felspar, while felspar is incapable of scratching quartz. Hence, we infer, that quartz is the harder of the two minerals. It is difficult to convey an idea of the relative hardness of minerals by a long description. ‘The method first put in practice by Kirwan, of using figures for that purpose, is more convenient than any other. He distinguished the relative hardness of minerals into 10 different degrees, that of the diamond the hardest mineral in nature being denoted by 10. Mohs has adopted the same plan, though he has neglected to mention the source whence he derived his first idea of it. But he has given us a mineral whose hardness is denoted by each of his figures. Every mineral is supposed to possess the hardness denoted by the figure, or a hardness intermediate between some two of the numbers, which, of course, will be denoted by a fraction. ‘The following table will render the nomenclature of hardness sufficiently intelligible :— 1 denotes the hardness of Tale. 26) seek 0 aleh Rocksalt, gypsum. ok... so Mee Calcareous spar. Bayt. aE exe Fluor spar. Bupee. ea, .. Apatite or phosphate of lime. Ris. ae -~ elspar or adularia. Aibhestes Ie ae Rock crystal. aay ae it iiss, Sil A LOTR Ont es bre Corundum. Loge wud isd Diamond. These minerals are all easily procurable, and therefore may be kept on purpose, to serve as objects of comparison. In trying the hardness of a mineral we should avoid apply- ing a sharp pointed mineral to it for that purpose, otherwise we may sometimes be led to consider it as softer than it really is. A good way to judge of the comparative hardness of two minerals is to draw the file over each; if there be a difference