Diamond

The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral. Its lustrous faces also indicate that this crystal is from a primary deposit.
Main diamond producing countries
Theoretically predicted phase diagram of carbon.
Diamond unit cell, showing the tetrahedral structure
One face of an uncut octahedral diamond, showing trigons (of positive and negative relief) formed by natural chemical etching
The extreme hardness of diamond in certain orientations makes it useful in materials science, as in this pyramidal diamond embedded in the working surface of a Vickers hardness tester.
Brown diamonds at the National Museum of Natural History in Washington, D.C.
The most famous colored diamond, the Hope Diamond
Geologic provinces of the world. The pink and orange areas are shields and platforms, which together constitute cratons.
Diavik Mine, on an island in Lac de Gras in northern Canada
Eclogite with centimeter-size garnet crystals
Red garnet inclusion in a diamond.
Age zones in a diamond.
Diagram of a volcanic pipe
Double diamond discovered in the Ellendale Diamond Field, Western Australia
A round brilliant cut diamond set in a ring
Diamond exports by country (2014) from Harvard Atlas of Economic Complexity
Diamond polisher in Amsterdam
The Darya-I-Nur Diamond—an example of unusual diamond cut and jewelry arrangement.
Diamond Balance Scale 0.01 - 25 Carats Jewelers Measuring Tool
A scalpel with synthetic diamond blade
Close-up photograph of an angle grinder blade with tiny diamonds shown embedded in the metal
A diamond knife blade used for cutting ultrathin sections (typically 70 to 350 nm) for transmission electron microscopy
Siberia's Udachnaya diamond mine
Synthetic diamonds of various colors grown by the high-pressure high-temperature technique
Colorless gem cut from diamond grown by chemical vapor deposition
Gem-cut synthetic silicon carbide set in a ring
Extremely rare purple fluorescent diamonds from the Ellendale L-Channel deposit in Australia

Solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic.

- Diamond

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Thermal conductivity

Measure of its ability to conduct heat.

Experimental values of thermal conductivity
Exhaust system components with ceramic coatings having a low thermal conductivity reduce heating of nearby sensitive components

Of all materials, allotropes of carbon, such as graphite and diamond, are usually credited with having the highest thermal conductivities at room temperature.

Synthetic diamond

Synthetic diamonds of various colors grown by the high-pressure high-temperature technique
Moissan trying to create synthetic diamonds using an electric arc furnace
First synthetic diamonds by ASEA 1953
A belt press produced in the 1980s by KOBELCO
A scalpel with single-crystal synthetic diamond blade
Schematic of a belt press
Schematic of a BARS system
Free-standing single-crystal CVD diamond disc
Electron micrograph (TEM) of detonation nanodiamond
Diamonds in an angle grinder blade
Colorless gem cut from diamond grown by chemical vapor deposition

Synthetic diamond (also called laboratory-grown, laboratory-created, man-made, artisan created, or cultured diamond) is diamond that is produced in a controlled technological process (in contrast to naturally formed diamond, which is created through geological processes and obtained by mining).

Allotropy

Property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements.

Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in crystalline structure.
Phase diagram of the actinide elements.

For example, the allotropes of carbon include diamond (the carbon atoms are bonded together to form a cubic lattice of tetrahedra), graphite (the carbon atoms are bonded together in sheets of a hexagonal lattice), graphene (single sheets of graphite), and fullerenes (the carbon atoms are bonded together in spherical, tubular, or ellipsoidal formations).

Metastability

Intermediate energetic state within a dynamical system other than the system's state of least energy.

A metastable state of weaker bond (1), a transitional 'saddle' configuration (2) and a stable state of stronger bond (3).

As another example, diamond is a stable phase only at very high pressures, but is a metastable form of carbon at standard temperature and pressure.

Mohs scale of mineral hardness

Qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material.

Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale

As the hardest known naturally occurring substance when the scale was designed, diamonds are at the top of the scale.

Diamond anvil cell

High-pressure device used in geology, engineering, and materials science experiments.

Schematics of the core of a diamond anvil cell. The culets (tip) of the two diamond anvils are typically 100–250 microns across.
The first diamond anvil cell in the NIST museum at Gaithersburg. Shown in the image above is the part which compresses the central assembly.
Researcher using a diamond anvil cell to study materials under deep Earth conditions.
Conditions achievable using different methods of static pressure generation.

A DAC consists of two opposing diamonds with a sample compressed between the polished culets (tips).

Cubic zirconia

Cubic crystalline form of zirconium dioxide (ZrO2).

A round brilliant-cut cubic zirconia
Worker monitoring melting zirconium oxide and yttrium oxide in an induction-heated "cold crucible" to create cubic zirconia
One face of an uncut octahedral diamond, showing trigons (of positive and negative relief) formed by natural chemical etching
Purple cubic zirconia with checkerboard cut
Multi-color cubic zirconia
Three-tone cubic zirconia gems
Yellow cubic zirconia

Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important competitor for diamonds since commercial production began in 1976.

Cleavage (crystal)

Tendency of crystalline materials to split along definite crystallographic structural planes.

Green fluorite with prominent cleavage
Biotite with basal cleavage
Miller indices {h k ℓ}

Diamond and graphite provide examples of cleavage.

Graphite

Crystalline form of the element carbon.

Graphite specimen
Theoretically predicted phase diagram of carbon
Molar volume against pressure at room temperature
Graphite plates and sheets, 10–15 cm high; mineral specimen from Kimmirut, Baffin Island
Grey Knotts mountain in the English Lake District. The graphite mine was just up the valley to the left; the hamlet of Seatoller can be seen at right.
Graphited Wood Grease 1908 ad in the Electric Railway Review
Graphite pencils
Structure of CaC6
Large graphite specimen. Naturalis Biodiversity Center, Leiden, Netherlands.
Graphite output in 2005
Scanning tunneling microscope image of graphite surface
Side view of ABA layer stacking
Plane view of layer stacking
Alpha graphite's unit cell

Under high pressures and temperatures it converts to diamond.

Allotropes of carbon

Capable of forming many allotropes due to its valency.

Two familiar allotropes of carbon: graphite and diamond.
Eight allotropes of carbon:
(a) diamond,
(b) graphite,
(c) lonsdaleite,
(d) C60 buckminsterfullerene,
(e) C540 fullerite
(f) C70 fullerene,
(g) amorphous carbon,
(h) zig-zag single-walled carbon nanotube.
Missing: cyclocarbon, carbon nanobuds, schwarzites, glassy carbon, and linear acetylenic carbon (carbyne)
Computer models of stable nanobud structures
A large sample of glassy carbon.
The K4 crystal
Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in structure.

Well-known forms of carbon include diamond and graphite.