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COMMENTARY
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is due to the impure steatite from which they were made or whether it is the result of use or of some artificial treatment such as the one that has just been described.
43. others can be carved with iron, but only with rather blunt tools.
In spite of the lacunae in the text, it is easy to understand the paradoxes which Theophrastus mentions in this and most of the following section. He is evidently puzzled by the contrast between the hardness of mineral substances and the ease with which they can be split or broken. Many minerals or rocks cannot be scratched or cut by ordinary iron tools because of their surface hardness, yet because of their low cohesive strength they can be split or chipped easily by blows from a blunt iron tool. However, one might expect a priori that because they are hard they ought also to resist forces that tend to break them. As is well known, even diamond, the hardest of minerals, can be split with no great difficulty. When one mineral can easily scratch or cut another, the difference in their cohesive strength may sometimes be such that the harder one can be split more readily than the softer one, if the tool is made of a material with a lower surface hardness than either of the minerals. Theophrastus was apparently the first writer to call attention to these matters. It was not until the time of Mohs (1773-1839) and other modern mineralogists that differences in hardness became important criteria for classifying and identifying minerals.
The text in this section is so corrupt that it cannot be emended with certainty. But some interesting emendations suggested by Stephanides and others have been combined to form a possible reconstruction of it. These appear in a footnote referring to section 43 of the translation.
44. the stone with which seals are carved.
That this was corundum, native crystalline aluminum oxide, particularly the impure form called emery, is highly probable. The strongest argument for this view is that corundum was the only mineral available to the Greeks that was hard enough for engraving varieties of quartz or other hard stones that were com-
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• 147·
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