The following information is taken from ICA - Gem Bureau, Idar-Oberstein.

Ruby is actually red corundum (all other corundums are sapphires)and is considered the king of gemstones having hardness (9 on the Mohs scale--second only to diamonds), magnificent color and brilliance. India was long considered the ruby's classical country of origin. Rubies are made up of aluminium oxide and chrome as well as very fine traces of other elements - depending on which deposit it was from. Rarely are rubies found in any mine, hence their amazing value. Some of the best rubies today come from Myanmar, though lesser qualities may be found in Thailand, Pakistan and Tibet. Large crystal rubies are also found in Mysore, India. These are also used in jewelry as cabochons..Pearls can be black, brown, gray, rose, red, blue, green, purple, yellow, and white. No one knows exactly how pearls develop their color, since one oyster may produce pearls of several different hues simultaneously.