Hardness

A lesson in hardness— A stone’s hardness is measured on a scale called the Moh’s scale. The scale measures from 1 (talc) to 10 (diamond).  A small incomplete list follows that tables some of the common jewelry stones and their relative hardness.   

  • Corundum, of which ruby and sapphire are composed--9  
  • Chrysoberyl 8.5  
  • Topaz --8 
  • Emerald has a hardness of about 7.5  
  • Garnet 7.25 to 7.5 
  • Zircon 7.5 
  • Moonstone 7 
  • Quartz, which includes amethyst, prasiolite, ametrine, and citrine-- grades at 7, and is the softest translucent material which is recommended for general jewelry usage as a gemstone.      
  • There are a few gemstones which are translucent, and therefore usually faceted. These include: 
  • Peridot 6.5 to 7 
  • Demantoid garnet at 6.5 
  • Zoisite including tanzanite 6 
  • Sphene 5 to 5.5    

Gems which are opaque do not show surface scratches as badly as faceted translucent stones, and therefore do not need to be as hard. Most opaque stones are polished into cabochons, with smooth rounded surfaces, as opposed to flat facets. Such gemstones include 

  • Turquoise at 6  
  • Opal 5.5 to 6 
  • Coral 3.5  
  • Pearl 2.5 to 3.5 
  • Amber 2 to 2.5 

All of the above are considered delicate materials and should be treated as such.