I can only think of three; ruby, jade and opal. is this binweevils right, ... well it could be any four letter word.... stones... so do the down first so you get the first letter of the stone... is...
Four ish (just a guess)
rock
You tell me loser :P
sardius,topaz,beryl,diamond
Gems and Stones in India
Learn about Judo and Jewellery
Bermuda's Ancient Caves
Paving Stones Placement