Of the natural gem materials, corundum is second only to diamond in hardness. Ruby is the red variety of corundum and it occurs as bright red, red, purplish or brownish-red and deep pinkish-red colours. The word "ruby" comes from the Latin word ruber, which means red. According to the story of Marco Polo, Kublai Khan offered the King of Ceylon a city in exchange for a large ruby. According to legend, the owner of a ruby is assured a life of peace and plenty. Ruby is the birthstone for those born in July. Ruby is used to celebrate the fifteenth and fortieth wedding anniversaries.