What determines the value of a gemstone?

By definition a gemstone is beautiful and durable enough to use as
personal adornment and the embellishment of our personal possessions.
To qualify as a gemstone, all the minerals and other materials must possess
at least three of the six main characteristics that are classically considered
to be desirable in a gemstone, these are beauty, durability, and rarity.
The others are fashion, special properties, and individual taste.

• Beauty
  Beauty is an intangible property with most people agreeing that the gemstone’s beauty is derived from the strength and purity of colour or clarity of the stone with strong reflecting, refracting and light dispersing properties.
• Cut
  The proper cutting or faceting of a gemstone emphasises its inherent colour and tends to give the stone more sparkle which enhances its beauty and desirability.
• Shape
  Some gemstones naturally occur in certain typical shapes or lend themselves to be cut into certain shapes. Emeralds, for example, lend themselves to being cut into oblong or octagonal shapes, so that an oblong shape with its corners cut to form an octagon is known as an emerald cut.
• Durabilty
  A stone must be able to resist wear, the abrasiveness of dust and knocking or rubbing against other material. The stone must be capable of lasting a long time without alteration of colour
• Rarity
  A gemstone is as beautiful and as attractive whether it is common or rare. The rarity of the gem can be affected by supply and demand and by fashion and the scarcity of the source material. The status value of gemstones is increased by their rarity, not the aesthetic value.
• Fashion
  What the celebrities wear can play a big part in determining whether a gemstone is in demand or not.
• Special properties
  Gemstones are believed to have special powers or vibrations that are beneficial to us. So we include the categories of health, superstition, religion and social custom when looking to own a beautiful gemstone.

Gemstones overview
What is a gemstone?
Why buy a coloured gemstone?
What determines the value of a gemstone?