Diamond

Hardness: 10 (Mohs scale), Color: Typically colorless, but can be yellow, brown, green, blue, pink, red, Luster: Adamantine (bright, reflective, like a diamond), Crystal structure: Isometric (cubic), Cleavage: Perfect octahedral (splits along four planes), Specific Gravity: 3.5-3.53

Formed deep within the Earth's mantle (100-200 km deep) under extremely high pressure (45-60 kilobars) and high temperature (900-1,300 °C) conditions. They are brought to the surface through volcanic eruptions by kimberlite and lamproite pipes. Most natural diamonds are between 1 billion and 3.5 billion years old.

Primarily used as gemstones in jewelry due to their brilliance, durability, and rarity. Industrial uses include abrasives (cutting, grinding, drilling), polishing, and in specialized tools and electronics due to their extreme hardness and thermal conductivity.

Diamonds are the hardest known natural material. They are metastable, meaning graphite is actually the more stable form of carbon at standard conditions, but the conversion rate from diamond to graphite is extremely slow. The word 'diamond' comes from the ancient Greek 'adámas' meaning 'unbreakable'. The largest rough diamond ever found was the Cullinan Diamond, weighing 3,106.75 carats (621.35 g).

In the field: While diamonds are rarely found in situ in their source rocks (kimberlite/lamproite), they are often found in alluvial deposits. They can be identified by their extreme hardness (scratches all other minerals), high specific gravity, and characteristic adamantine luster. Common locations include Russia, Botswana, Canada, Australia, and South Africa. For collectors, looking for rough diamond crystals might involve searching in areas known for kimberlite pipes or sorting through gravel in alluvial deposits.