Precious Gemstones versus Semi-precious Gemstones

What is the difference between precious gemstones and semi-precious?  First, let  us clarify that a gemstone is a jewelry-grade mineral and not just any old rock.  To be considered precious a gemstone must meet three requirements:  high MOHS hardness, fineness of color, and purity of chemical make-up.   The four precious-graded jewelry gemstones are diamond, emerald (from Beryl family), ruby and sapphire.


Precious Gemstones

• Diamonds are considered precious, but they are an exception to the "color:" requirement as "white" or clear diamonds are typically more desirable, especially for engagement rings and wedding sets.  The quality of finished diamonds is based on the four C's: carat, clarity,  color, and cut.  Many jewelers also suggest a 5th C for Confidence that it is coming from a reputable source who has properly graded the diamond.
• Emeralds are precious, but you never hear anyone refer to any of the other beryls (blue aquamarine, white goshenite, pink morganite, yellow helidore) as precious.  Why not?   in ancient times, finding a quality green stone was rare, so emerald was only owned by royalty and the rich.  Today, it is not so hard to find and mine.  Some of the other colors of beryl are more rare than emerald.  So a gemstone being rare has nothing to do with it being considered precious now.
• Rubies are corundum that are specific shades or red and therefore considered precious.  However, not all corundums are precious, since some are of lower quality or lack the chemical make-up to be called Ruby or Sapphire.  Honest jewelry dealers will typically list these non-precious varieties as red, blue, or green corundum.
• Sapphires are also considered precious in the past.  Many  colors are classified as sapphires - that means the rarer fancy colors (anything other than standard blues) should be considered precious.  The rarest and most expensive blue colors are Ceylon and Cashmere.  

Semi-precious gemstones will only have one or two of the gemstone requirements for jewelry. Any gemstone besides the four above should be considered semi-precious.  Whether or not a stone is rare or natural, is no longer considered in defining it as precious.  The precious stones above were rare finds in ancient times,but come from many mines around the word now.  Currently, there are more semi-precious stones that are considered rare.  Rare typically means the stones only come from one place or are no longer available because they have been mined-out.

Gemstones from both precious and semi-precious classifications may be found in the lists containing anniversary stones, birthstones and zodiac stones.