You tell me loser :P
5 precious stones I know are the Diamond, Ruby, Emerald, Sapphire, and Opal.
They are expensive due to their beauty, rarity (or perceived rarity), and cost to produce them. Tight control of supply of precious stones (for example De Beers and diamonds) also increases the price...
topaz tourmaline tiger's eye tanzanite
sapphires can be blue and are commonly known gemstone