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DIAMOND |
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| Diamond
is one of the natural allotropes of carbon (the main allotrope
being graphite; see also allotropes of carbon). The hardest
of naturally occurring materials, diamonds cut into multi-faceted
shapes are among the most prized gemstones of jewelry,
and find use in industrial applications as well. |
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| Contents |
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1
Properties
1.1 Hardness and crystal structure
1.2 Toughness
1.3 Optical properties
1.4 Electrical properties
1.5 Thermal properties
1.6 Composition and color
2 The diamond industry
2.1 Cut
2.1.1 Cut Grading
2.2 Clarity
2.3 Color
2.4 Sources
3 Symbolism of diamonds
4 Related terms
5 Famous diamond cutters
6 Famous stones
7 See Also
8 External links
8.1 Labs, Cut, and General Links
8.2 Chemistry and Artificial Diamonds
8.3 Natural Sources and Marketing
9 Further reading
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| Diamond
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A
scattering of "brilliant"
cut diamonds shows off the many reflecting
facets.
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| General |
| Category |
Native
Nonmetal, Mineral |
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| Chemical
formula |
Carbon,
C |
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| Identification |
| Color |
Most
often colorless to white. Rarely
pink, yellow, orange, green or
blue. |
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| Crystal
habit |
Octahedral,
spherical or massive |
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| Luster |
Adamantine
to greasy |
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| Refractive
index |
index
2.417 |
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| Specific
gravity |
3.516
- 3.525 |
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| Major
varieties |
| None |
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| Properties |
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| Diamond is
a transparent, optically isotropic crystal with a refractive
index of 2.417, a high dispersion of 0.044, and a specific
gravity of 3.52. |
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| Hardness
and crystal structure |
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The diamond
crystal bond structure gives the gem its hardness and
differentiates it from graphite.
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| Sometimes known
as adamant, it is the hardest known naturally occurring
material, scoring 10 on the old Mohs scale of mineral
hardness. The material boron nitride, when in a form structurally
identical to diamond, is nearly as hard as diamond; a
currently hypothetical material, beta carbon nitride,
may also be as hard or harder in one form. Furthermore,
it has been shown 1 (http://www.mrs.org/publications/jmr/jmra/articles/1997/nov/p03109.pdf)
2 (http://www.mtu-net.ru/nanoscan/files/article_03.pdf)
that ultrahard fullerite (C60) (not to be confused with
P-SWNT Fullerite) when testing diamond hardness with a
scanning force microscope can scratch diamond. In turn,
using more accurate measurments, these values are now
known for diamond hardness. A Type IIa diamond (111) has
a hardness value of 167 GPa (±6) when scratched
with an ultrahard fullerite tip. A Type IIa diamond (111)
has a hardness value of 231 GPa (±5) when scratched
with a diamond tip which leads to hypothetically inflated
values. |
The diamond derives its name from the
Greek adamas, "untameable" or "unconquerable",
referring to its hardness.
Diamonds typically crystallize in the
cubic crystal system and consist of tetrahedrally bonded
carbon atoms. A second form called lonsdaleite with
hexagonal symmetry is also found. The local environment
of each atom is identical in the two structures. Cubic
diamonds have a perfect octahedral cleavage, which means
that they have four cleavage planes. Diamonds occur
most often as euhedral or rounded octahedra and twinned
octahedra known as macles. Other forms include dodecahedra
and cubes. Diamonds are commonly found coated in nyf,
a gum-like skin. Their fracture may be step-like, conchoidal
(shell-like, similar to glass) or irregular.
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Toughness
Unlike hardness, which only denotes resistance to scratching,
diamond's toughness is only fair to good. Toughness
relates to its ability to resist breakage from falls
or impacts. Particular cuts of diamonds are more prone
to breakage, and thus may be uninsurable by reputable
insurance companies. The culet is a facet designed exclusively
to resist breakage. Extremely thin, or very thin girdles
are also prone to much higher breakage.
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Optical
properties
The luster of a diamond is described as adamantine,
which simply means diamond-like. Some diamonds exhibit
fluorescence of various colors under long wave ultra-violet
light, but generally bluish-white, yellowish or greenish
fluorescence under X-rays. Some diamonds, particularly
Canadian diamonds, show no fluorescence. Diamonds have
an absorption spectrum consisting of a fine line in
the violet at 415.5 nm. Colored stones show additional
bands. Brown diamonds show a band in the green at 504
nm, sometimes accompanied by two additional weak bands
also in the green.
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| Adamas Gemological
Laboratory (http://www.gis.net/~adamas)
makes spectrophotometer machines that can distinguish
natural, artificial, and color-enhanced diamonds. Diamond
has an index of refraction of 2.42 in the visible spectrum. |
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| Electrical
properties |
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| Except for
most natural blue diamonds which are semiconductors, diamond
is a good electrical insulator. Natural blue diamonds
recently recovered from the Argyle mine in Australia have
been found to owe their color to an overabundance of hydrogen
atoms: these diamonds are not semiconductors. Natural
blue diamonds containing boron and synthetic diamonds
doped with boron are p-type semiconductors. If an n-type
semiconductor can be synthesized, electronic circuits
could be manufactured of diamond. Worldwide research is
in progress, with occasional successes reported, but nothing
definite. In 2002 it was reported in the journal Nature
that researchers have succeeded in depositing a thin diamond
film on a diamond surface which is a major step towards
manufacture of a diamond chip. In 2003 it was reported
that NTT developed a diamond semiconductor device[1] (http://www.eetimes.com/at/hpm/news/OEG20030822S0005).
In April of 2004 Nature reported that below the superconducting
transition temperature 4 K, boron-doped diamond synthesized
at high temperature and high pressure is a bulk, type-II
superconductor[2] (http://www.nature.com/nature/journal/v428/n6982/pdf/nature02449.pdf).
In October of 2004 superconductivity was found to occur
in heavily boron-doped microwave plasma-assisted chemical
vapor deposition (MPCVD) diamond below the superconducting
transition temperature of 7.4 K[3] (http://content.aip.org/APPLAB/v85/i14/2851_1.html)
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| Thermal
properties |
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| Unlike most
electrical insulators, diamond is a good conductor of
heat because of the strong covalent bonding within the
crystal. Most natural blue diamonds contain boron atoms
which replace carbon atoms in the crystal matrix, and
also have high thermal conductance. Specially purified
synthetic diamond has the highest thermal conductivity
(2000–2500 W/(m·K), five times more than
copper) of any known solid at room temperature. Because
diamond has such high thermal conductance it is already
used in semiconductor manufacture to prevent silicon and
other semiconducting materials from overheating. |
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