Sapphire is the birth stone for those born in September. Corundum, with traces of iron, titanium, chromium, vanadium or magnesium responsible for the color. Sapphires are 9 on the moh's scale, right behind diamond ( moh's10)
Sapphire is said to bring peace and prosperity to those that own it.
The most expensive sapphire to my knowledge ( The Blue Belle) sold for approx. $17,00,000.00 at auction in 2014. Only in fairly modern times, after a massive advertising campaign, have diamonds become the usual stone for engagements. Before that sapphires ruled. Indeed, Prince William gave Kate Middleton a magnificent sapphire.