Gems and precious metals are gifts of nature, which need special care. Even
though
a gem may be millions of years old, once mined and worn, it is exposed to conditions
and chemicals that can damage it.
Hardness is based on a gem-trade standard called the Mohs Scale, developed in the
early 19th century. The scale is structured so that material rated at each higher
number can scratch substances with lower numbers. Diamonds are rated the highest,
at 10; rubies and sapphires are Mohs 9; emeralds and topaz, 8; and garnets, tourmalines
and quartz, 7. Anything softer than a 7 can be scratched, including opal, turquoise,
lapis lazuli, coral, pearl.
Gold, silver, and platinum are only Mohs 2-1/2 to 4, which means that they require
special care when wearing, storing, or cleaning.
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