Birthstones

Birthstones for each month:

January – dark red – Garnet.
February – purple – Amethyst.
March – pale blue – Aquamarine (or dark green & red – Bloodstone).
April – white or clear – Diamond or Rock Crystal.
May – bright green – Emerald or Chrysoprase.
June – cream – Pearl or Moonstone (or green – Alexandrite).
July – red – Ruby or Carnelian (or black – Onyx).
August – pale green – Peridot (or white & reddish brown – Sardonyx).
September – deep blue – Lapis Lazuli or Sapphire.
October – variegated – Opal or Tourmaline.
November – yellow – Topaz or Citrine.
December – sky blue – Turquoise or Zircon.

See some examples below:
Birthstones
Notice that the Alexandrite shown for June looks purple. This is an unusual gemstone with colour changing properties and appears green under daylight, but quite a different colour under artificial light!