A gemstone’s quality has three basic factors: beauty, durability and rarity. Beauty is first, color being 50% of its value, clarity 30% and cut 20%. Not often considered, good proportions, symmetry and polish can result in a stone’s beauty being enhanced with brilliance and dispersion. A large percentage of colored gemstones are cut in India, notorious for retaining weight by leaving thick bottoms, consequently a dull-looking stone. Those that are of fine quality are generally re-cut after exportation.
Durability is second. Not that a stone needs be indestructible but that it will withstand ordinary wear.
Rarity, although third, frequently determines price. Demand is based on rarity and fashion. Amber was once very fashionable—second most important import to USA. It lay dormant for decades until “Jurassic Park!”
Tradition also affects a stone’s value—making it precious. It is taught to us through historic example. The book of exodus tells us that around 5000 BC, the Lord told the Israelites to make a breast plate for Aaron the High Priest. Twelve stones with the names of the twelve tribes were inscribed on it so that Aaron would bear their names before the Lord as a memorial. The original birthstone list is taken from this example. It was changed in 1937 with stones of greater popularity. In recent times, a couple of alternates have been added, Moonstone to join Pearl, Alexandrite in June and Tanzanite with Turquoise and Zircon in December.