Why are there two birthstones for April? This is because, according to the National Association of Jewelry, Diamonds are the traditional or modern birthstone for April, whereas Sapphire was popularly worn as the month's birthstone during antiquity for protection and strength. Diamond is a precious mineral that is hard and made of pure carbon. It has a crystal lattice shape and has the highest durability rate of hardness on the Mohs scale, which is ten. Whereas, a transparent or translucent gem variety of the corundum mineral, Sapphire is known for its color, clarity, and durability on the hardness scale of (9) Mohs.