Natural diamonds are formed deep within the Earth's mantle under extreme pressure and temperature over millions of years, making each one unique with its own history and origin. This long and complex formation process contributes to their rarity, which is a key factor in their higher price point. Because of their scarcity, natural diamonds generally hold greater resale value, although the secondary market for diamonds remains relatively limited. Additionally, their rarity makes them more expensive, particularly for larger stones or those with higher quality cuts, clarity, and color, further enhancing their perceived worth.