Blue diamonds are a rare type of diamond known for their stunning blue color, which is caused by the presence of boron during their formation. These gemstones are graded based on their hue, tone, and saturation, with the most valuable stones displaying a deep, vivid blue. Blue diamonds are often used in high-end jewelry and are sought after by collectors. One of the most famous blue diamonds is the Hope Diamond, which is known for its striking color and intriguing history. Blue diamonds are typically more expensive than traditional colorless diamonds due to their rarity and unique beauty, making them a symbol of luxury and prestige.