Diamond

Diamond: The Quintessence of Carbon and Pressure Diamond is the only gemstone composed of a single element: carbon (C). Its cubic crystal structure, where each atom is bonded to four others by extremely strong covalent bonds, gives it a Mohs hardness of 10, placing it at the very top of the mineral hierarchy.

Geological Formation and Magmatic Ascent Diamonds are not formed in the Earth's crust but in the upper mantle, at depths exceeding 150 km, under pressures of more than 50 kilobars.

• Mantle Messengers: They are transported to the surface by ultra-potassic magmas called kimberlites or lamproites. These eruptions are so rapid that they prevent the diamond from transforming into graphite (its stable form at low pressure).

• Optical Properties: Its "adamantine" luster stems from a very high refractive index (2.417) and strong dispersion (0.044). The latter separates white light into its spectral components, creating the gemstone's characteristic "fire."

The Chemistry of Fancy Colored Diamonds While a pure diamond is perfectly colorless (Type Ia or IIa), the incorporation of foreign atoms alters its electronic properties:

• Nitrogen (N): The most common impurity, responsible for yellow to orange hues.

• Boron (B): A rare element that gives the diamond its blue color and semi-conductive properties.

• Plastic Deformations: Pink and red hues often result from glides within the crystal lattice due to extreme tectonic pressures, rather than a chemical element.

Laboratory Expertise: Natural vs. Synthetic During expertise, we distinguish between natural diamonds and laboratory-grown diamonds (LGD). Although chemically and physically identical, lab-grown diamonds (produced via HPHT or CVD methods) exhibit different growth signatures (fluorescence, metallic inclusions, or growth patterns) detectable only with advanced instrumentation.

• Fragility: Despite its hardness, diamond possesses perfect cleavage in four directions. A sharp blow on a cleavage plane can shatter the stone instantly.