The hardest stone is colorless although there are also blue, yellow and pink varieties; it is the most renowned precious stone.
sapphire
This stone can be blue, pink, orange, yellow, green, purple or even colorless; the most sought-after color is purplish-blue.
ruby
The rarest of all precious stones is extremely hard; its color varies from a bright pinkish-red to a purplish red, which is the most sought-after color.
emerald
Stone whose color varies from greenish-yellow to greenish-blue; an emerald’s value is based more on its color than on its purity.
