Diamond
The atoms in a diamond arrange themselves into a crystal structure called diamond cubic. Each carbon atom bonds to four nearest neighbors, forming tetrahedra that are rigid and strong. This arrangement gives diamond the highest hardness of any natural material. It also possesses the greatest number of atoms per unit volume among known substances. The density ranges from 3150 to 3530 kilograms per cubic metre for natural diamonds. Pure diamond reaches 3520 kg/m³. These properties make it both the hardest and least compressible substance known. Yet despite its strength, diamond is brittle and can fracture under forceful impact. Its toughness measures between 50 and 65 MPa·m¹/². This value is good compared to other ceramics but poor against engineering alloys. Diamond has high thermal conductivity and sound velocity. It resists most corrosive substances and shows excellent biological compatibility.
Most natural diamonds formed at depths between 150 and 250 kilometers within Earth's mantle. They originated as carbon-containing fluids dissolved minerals and replaced them with new crystals. Some diamonds came from even deeper zones, reaching 330 to 800 kilometers below the surface. These deep formations occurred hundreds of millions to billions of years ago. Kimberlite magma later transported them upward at speeds of 4 to 20 meters per second. Volcanic eruptions deposited these stones into igneous rocks called kimberlites and lamproites. Most diamonds are between 1 billion and 3.5 billion years old. The kimberlite pipes themselves are much younger, typically tens of millions to 300 million years old. No kimberlite has erupted in human history. The Argyle mine in Australia stands out as an exception, located in a mobile belt rather than stable craton. Popigai impact structure in Russia may hold trillions of carats formed by asteroid collision.
The name diamond derives from Greek adamas meaning proper unalterable or untamed. Diamonds were first recognized and mined in India along rivers Penner Krishna and Godavari. Significant alluvial deposits existed there many centuries before recorded history. Evidence suggests Indians knew diamonds for at least 3000 years possibly up to 6000 years. They used early forms as religious icons and engraving tools. In 1772 French scientist Antoine Lavoisier concentrated sunlight rays on a diamond using a lens. He placed it in oxygen atmosphere and observed only carbon dioxide produced. This proved diamond composed entirely of carbon. English chemist Smithson Tennant repeated the experiment in 1797. He demonstrated burning diamond and graphite released identical gas amounts establishing chemical equivalence. India led global production until mid-18th century when Brazil discovered non-Indian sources in 1725. Commercial potential exhausted Indian deposits by late 1700s.
Diamond's extreme hardness enables cutting glass and other materials including itself. Industrial-grade diamonds make up eighty percent of mined output annually. These stones equal about five thousand metric tons yearly. Synthetic diamonds reached nine hundred million carats production in 2014 with ninety percent made in China. Diamond-tipped drill bits and saws use this property extensively. Powdered diamond serves as abrasive material for polishing operations. High thermal conductivity makes diamond suitable heat sink for integrated circuits. Laboratories employ diamond anvil cells containing samples under pressures exceeding one hundred gigapascals. Some experiments reach ten million atmospheres or one terapascal. Blue natural semiconductors contain boron impurities enabling electrical conduction unlike typical insulating diamonds. Thin needles can vary electronic band gap from normal 5.6 eV near zero through mechanical deformation. Quantum data storage becomes possible using high-purity wafers five centimeters diameter containing three parts per million nitrogen.
Four characteristics known informally as four Cs describe gemstone quality: carat weight cut color clarity. One carat equals 0.2 grams. Wholesale trade concentrates heavily; ninety-two percent of world diamonds cut and polished in Surat India during 2003. Antwerp handles eighty percent rough diamonds fifty percent cut stones plus over half combined categories. De Beers founded by Cecil Rhodes in 1888 dominated industry throughout twentieth century. By 2013 company market share dropped to thirty-eight percent value terms less volume. Jwaneng mine Botswana produces between two and three million carats annually. Rio Tinto owns Argyle Diavik Murowa mines. In 2002 total market value reached nine billion dollars rough fourteen billion after cutting twenty-eight billion wholesale fifty-seven billion retail sales. Kimberley Process introduced 2002 aims prevent conflict diamond funding wars. Conflict diamonds constitute two to three percent traded globally according to International Diamond Manufacturers Association.
Laboratory methods create synthetic diamonds via high-pressure high-temperature processes or chemical vapor deposition. HPHT produces yellow stones caused by nitrogen impurities while CVD grows single crystals several millimeters size under low pressure below atmospheric level. Nearly all five thousand million carats produced yearly serve industrial purposes. Around fifty percent natural mined diamonds end up industrial use instead gemstone markets. Synthetic manufacturers expenses average lower than mining companies costing forty to sixty US dollars per carat for natural versus cheaper synthetic alternatives. Cubic zirconia remains most common simulant though moissanite silicon carbide costs more produce synthetically. Electronic thermal probes identify real diamonds separating them from imitations within two to three seconds. Optical techniques distinguish natural from synthetic varieties using fluorescence spectroscopy microscopy luminescence. D-J colored diamonds screened through Swiss Gemmological Institute's Diamond Spotter tool. Perfect atomic crystals never found exist; both types always possess characteristic imperfections allowing differentiation.
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Common questions
What is the crystal structure of diamond?
Diamond atoms arrange themselves into a crystal structure called diamond cubic. Each carbon atom bonds to four nearest neighbors, forming tetrahedra that are rigid and strong.
How deep do most natural diamonds form within Earth's mantle?
Most natural diamonds formed at depths between 150 and 250 kilometers within Earth's mantle. Some diamonds came from even deeper zones reaching 330 to 800 kilometers below the surface.
When did Antoine Lavoisier prove diamond is composed entirely of carbon?
French scientist Antoine Lavoisier concentrated sunlight rays on a diamond using a lens in 1772. He placed it in an oxygen atmosphere and observed only carbon dioxide produced.
Which country led global diamond production until the mid-18th century?
India led global production until the mid-18th century when Brazil discovered non-Indian sources in 1725. Significant alluvial deposits existed there many centuries before recorded history.
What percentage of mined diamonds serve industrial purposes annually?
Industrial-grade diamonds make up eighty percent of mined output annually. Nearly all five thousand million carats produced yearly serve industrial purposes.