Diamond

Hardness: 10 (Mohs scale), Color: Colorless to faint yellow/brown (can be fancy colors), Luster: Adamantine, Crystal Structure: Cubic (Isometric), Cleavage: Perfect octahedral, Specific Gravity: 3.52

Formed under high-pressure, high-temperature conditions in Earth's mantle, typically at depths of 150-200 kilometers. Brought to the surface via kimberlite or lamproite volcanic eruptions. Most are 1 to 3.5 billion years old.

Used extensively in jewelry for its brilliance and hardness; industrial applications include cutting, grinding, and drilling tools; high-tech uses in heat sinks and optics.

Diamond is the hardest natural substance known. It is composed of a single element: Carbon. Famous specimens include the Hope Diamond and the Cullinan Diamond.

Identify by extreme hardness (scratches all other minerals), high refractive index, and thermal conductivity. Commonly found in kimberlite pipes or alluvial deposits in Africa, Russia, Canada, and Australia.