With its atoms grouped in what is known as a diamond cubic crystal structure, diamond is a solid form of the element carbon. The chemically stable form of carbon at room temperature and pressure is another solid form of carbon known as graphite, but diamond transforms to it very slowly. Due to its superior hardness and thermal conductivity, diamond is employed in many important industrial applications, including cutting and polishing equipment. They also allow materials to be subjected to pressures observed at great depths in the Earth in diamond anvil cells.
Few forms of impurities can contaminate diamond because of how rigidly the atoms are arranged in it (two exceptions are boron and nitrogen). About one impurity or flaw in a million lattice atoms gives diamond its various colors, including blue (from boron), yellow (from nitrogen), brown (from defects), green (from radiation exposure), purple, pink, orange, or red. Additionally, the optical dispersion and refractive index of diamond are both extremely high.
A billion to 3.5 billion years ago is when the majority of natural diamonds were formed. A handful have emerged from as deep as 800 kilometers, although the majority developed between 150 and 250 kilometers (93 and 155 mi) in the Earth's mantle (500 mi). Diamonds were created when carbon-containing fluids dissolved different minerals at high pressure and temperature. They were brought to the surface by volcanic eruptions hundreds to tens of millions of years ago and deposited in igneous rocks known as kimberlites and lamproites.
High-purity carbon may create synthetic diamonds under extreme pressure and temperature conditions, or chemical vapor deposition can grow them from hydrocarbon gases (CVD). Silicon carbide and cubic zirconia are two more substances that can be used to create imitation diamonds. The most popular methods for differentiating between real, fake, and synthetic diamonds include optical methods and thermal conductivity tests.