The birthstone most closely associated with the astrological sign of Gemini is the pearl. Although the emerald has been associated with the sign, the characteristics of the pearl reflect the traits of the sign more closely.
Gemini birthdays fall between May 21 and June 21. Because a larger portion of the month of June is involved in the Gemini sign, June's birthstone of pearl is used for this sign's birthstone. Other common birthstones associated with Gemini include the emerald, which is May's birthstone, and alexandrite, which is an alternative birthstone for June birthdays. The birthstone of pearl is believed to be associated with the planet Mercury and the trait of personal integrity. Pearl's other traits that line up with the sign are loyalty, faithfulness, friendship, purity and modesty. Gemini is said to be the sign of twins with its ruling element being air.