Tuesday, May 26, 2009

The ‘Mohs Scale'...and Why You Should Care

Devised by the German mineralogist Frederich Mohs (1773-1839), the oft-referred-to Mohs scale measures the relative hardness of ten minerals, numbered 1-10 -- chosen at the time because they were common and/or readily available.

The scale starts with talc (#1) a very soft and unstable substance. However, the scale is somewhat arbitrary and is not scientifically linear. For instance, while #9, corundum – a category that includes sapphire and ruby -- is twice as hard as #8 (topazes), the diamond (#10) is more than four times as hard as corundum.

  1. Talc (plastic)
  2. Gypsum (salt, fingernails, gold)
  3. Calcite
  4. Fluorite
  5. Apatite (copper coin, window glass)
  6. Orthoclase (includes moonstone & labradorite)
  7. Quartz (tourmaline, crystal quartz and all colored quartzes)
  8. Topaz (also beryl’s – emerald & aquamarine)
  9. Corundum (sapphire & ruby)
  10. Diamond

One can see why calcite -- #3 on the scale and therefore relatively soft -- was a favorite material for Egyptian sculptors. Also known as ‘Egyptian alabaster, calcite was used to create the canopic equipment that eventually contained the internal organs of individuals removed during the process of mummification (and which can be seen firsthand in many museums).

So – all very interesting you say…but why should I care about this? The biggest reason I think is the ‘ole gotcha, “caveat emptor.” Whenever one is purchasing gems it seem a good idea to be an educated buyer.

For instance, it’s become very popular for the public to attend gem fairs where they can purchase faceted stones to be set later. However, one should know, for instance, that although fluorite and apatite are both beautiful stones with a huge color range, they are not recommended for rings -- because they are soft enough to scratch easily or even crack. Therefore they should be used only for necklaces and/or earrings that don’t experience the same kind of wear.

On the other hand, quartzes (#7) are beautiful, come in a wide range of colors, are relatively inexpensive and -- can take a lot of daily wear.

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