Corundum is a crystalline form of aluminum oxide that is naturally clear but takes on color from impurities. Ruby gets its red color from chromium, while sapphire comes in various colors like blue and green due to iron and titanium. Corundum is called sapphire except when red, in which case it is ruby. A rare exception is padparadscha sapphire from Sri Lanka, which has a pinkish-orange hue. The document encourages purchasing rubies for July birthdays as they symbolize love, imagination, health, wealth and success.