Final answer:
Diamonds form under extreme heat and pressure in the Earth's mantle and are brought to the surface by volcanic eruptions in kimberlite pipes. They are thermodynamically unstable but kinetically stable at surface conditions. Diamonds are carefully extracted from silicate rock using specialized techniques.
Step-by-step explanation:
The geological conditions necessary for diamond formation require extreme heat and pressure, usually found deep within the Earth's mantle, about 140 to 190 kilometers (90 to 120 miles) below the surface. These conditions enable carbon atoms to bond in a lattice structure, resulting in the formation of diamonds. Thermodynamically, diamonds are unstable at Earth's surface conditions, but they are kinetically stable, which means they maintain their form over extremely long periods potentially millions to billions of years. Diamonds are brought to the Earth's surface through violent volcanic eruptions in deep-source volcanic pipes known as kimberlites or less commonly, lamproites.
The magma from such eruptions travels rapidly to the surface, carrying diamonds within it before they have a chance to transform into graphite. Once the magma cools and solidifies, the diamonds can be found encased within these types of igneous rocks. To chemically free a diamond encased in silicate rock without harming it one would typically use methods such as mechanical separation or careful chemical dissolution of the surrounding rock material that does not affect the diamond, because of its exceptional hardness and chemical resistance.