The emerald is a precious gemstone known for its striking green color and is a variety of the mineral beryl. It is one of the "big four" gemstones, alongside diamonds, rubies, and sapphires. The green color of emeralds is caused by trace amounts of chromium and sometimes vanadium in the crystal structure. Clarity: Almost all emeralds have some inclusions, or internal flaws, which are known as "jardin" due to their resemblance to garden-like patterns.