The Ruby gemstone is one of the four main precious gemstones. It is a red stone that rates 9 on the Mohs hardness scale. The Ruby crystal is a variety of corundum (aluminium oxide) and this is what gives the stone its red coloring. It is part of the hexagonal crystal system and is an expensive precious stone with a higher price for the quality of cut and carat. The Ruby is a popular gift for the 40th wedding anniversaries. The meaning of Ruby is protection and fortune. It is a root chakra and lower chakra stone.