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<p>[QUOTE=&quot;-jeffB, post: 1477603, member: 27832&quot;]Here&#039;s an interesting table that I can&#039;t quite believe I never came across before:</p><p><br /></p><p><a href="http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness#Intermediate_hardness" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness#Intermediate_hardness" rel="nofollow">Mohs scale of mineral hardness, with intermediate substances</a></p><p><br /></p><p>Some points of particular interest:</p><p><br /></p><p>Silver and gold have a hardness of 2.5 to 3. (0 is softest, 10 is hardest.) Copper&#039;s hardness is 3; steel comes in around 4-4.5.</p><p><br /></p><p>Tooth enamel comes in around 5.</p><p><br /></p><p>Glass and fused quartz are 6 to 7. That&#039;s what sand (or fine silica abrasive) would be, too.</p><p><br /></p><p>I don&#039;t know what the &quot;hardness&quot; of toothbrush bristles or a cloth would be, but it&#039;s not really relevant; what&#039;s more important is the stuff they might be dragging across the coin. Dirt, sand, leftover toothpaste -- all are <i>significantly</i> harder than any coin metal, and will definitely scratch.</p><p><br /></p><p>The surface of a coin is much more fragile than the surface of a glass, or the surface of a tooth, or even the surface of a car. More importantly, people examine a coin&#039;s surface more closely than they examine any of those other things.[/QUOTE]</p><p><br /></p>

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