The element Carbon (C, atomic number 6, atomic weight 12.011) is one of the most important of the chemical elements, being a basis for life itself and substantial quantities of human commerce.  Of its naturally-occurring and synthetic elemental forms, diamond possesses a certain ubiquity and unique standing, both because of its historic rarity and because of its many uses.  Diamond's covalently-bound crystal structure is such that its imperviousness to chemical and mechanical influences, along with its optical properties, create a material that has usefulness in industrial processes and as an aesthetic article of commerce and political consequence.  Diamond has assumed an important role in many diverse technological applications.  As a companion to carbon's other expressions, it has a quality that is as transcendent as it is complementary.

The element Carbon

The CRC Handbook of Chemistry and Physics, 57th Edition contains an article by C.R. Hammond (WEAST 77a) noting that Carbon, whose symbol is C, has atomic number 6 and atomic weight 12.011.  Carbon is understood to have formed by the nucleosynthetic fusion of 3 helium nuclei in the later stages of star formation, as described in Krane's Modern Physics (KRANE 83).  The Sargent-Welch Periodic Table of the Elements (SARGENT 79) cites an estimated melting point of 4100 K and boiling point of 4470 K, while Petrucci's General Chemistry (PETRUCCI 82) indicates that diamond melts above 3500 degrees C.

Diamond as a form of Carbon

Carbon appears naturally in the form of diamond, a material having a specific gravity of 3.15 - 3.53, depending upon variety, with gem diamonds at 3.513 at 25 degrees C (WEAST 77a).  Other forms of carbon include graphite and the "white" carbon formed on the planes of graphite under certain conditions, as noted in the CRC Handbook.  The entry at webelements.com (WINTER 03) refers to the more recently-discovered buckminsterfullerene, or C60, formed in the treatment of graphite by lasers.  See also the Molecule of the Month description at bris.ac.uk (LOCKE 96).

Diamond as a Crystal

The crystalline structure of diamond is that of a network covalent solid, established by strong covalent bonds between one carbon atom and another (PETRUCCI 82).  This is referred to as the "diamond structure".  It is one in which four carbon atoms define a tetrahedron with a 5th atom inscribed in its center.  The resulting material, as noted in the Physical Constants section of the CRC Handbook (WEAST 77b),  is a colorless, cubic-crystal solid, with an index of optical refraction of 2.4173.

Diamonds in nature

Diamond appears within the earth's crust principally within a formation known as kimberlite, a deposit created in "pipes" by ancient volcanoes.  It has been mined in South Africa, among other places, and diamonds have also been found on the ocean's floor, as off the Cape of Good Hope (WEAST 77a).  As noted in yourgemologist.com (JAMES 03), diamond deposits "are found world wide, probably more than DeBeers wants us to know".  A full discussion of the political and economic implications of diamond mining and marketing is outside the scope of this paper.

Perhaps as a nod to the future, Arthur C. Clarke, in 2061:  Odyssey Three (CLARKE 87), besides asserting the probability of diamonds in abundance within gas giant planets such as Jupiter, speaks of a day when a "space elevator" may be built, using diamond obtained in bulk as a construction material.

Artificial diamond

Aside from those diamonds found in nature, which Materials for Engineering indicate were the only source until after the middle of the 20th century, several tons per month are now being made artificially from graphite through the combined use of high pressure and high temperature (VANVLACK 82).  As indicated in a paper at uchicago.edu (CHEN 96), diamond can also be deposited as thin layer on silicon, in epitaxially-oriented growth, a process having extraordinary applications in electronics.

Industrial abrasives

Materials for Engineering (VANVLACK 82) states that diamonds have great value as a technical material, because of their extreme hardness.  Because of the strong covalent bonds, breaking or scratching a diamond requires that such bonds be broken; thus the wide use as abrasives (PETRUCCI 82).  The hardness, as indicated on the Mohs Scale, is 10 (VANVLACK 82), which makes it harder than other abrasive compounds such as boron carbide, silicon carbide, titanium carbide and tungsten carbide. Materials for Engineering further describes three forms of synthetic industrial diamonds of various toughnesses; high-impact strength (used for sawing granite), medium-impact strength (used for grinding eyeglasses) and low-impact strength (used for sharpening cemented-carbide tools).

Gemstones

As in the general public awareness discussed in yourgemologist.com, the diamond is "the most popular gemstone of all time"; "diamonds are a girl's best friend" (JAMES 03).  Clarke's suggestions as to diamond in bulk (CLARKE 87) would certainly render moot the current commerce in diamonds as a fashion accessory and a means of human emotional expression, but the varieties in cut, color and clarity (JAMES 03) are sufficient at present to create a marketplace of significant proportion.  The high refractive index of a diamond allows it to capture and reflect light in unique ways; thus the term "sparkler".  As shown by bluenile.com, this property, in combination with the geometry of the cut, makes for a presentation having appealing aesthetics (BLUENILE 03).  Such objective and subjective attributes make for a natural basis for the assignment of monetary value to assorted grades.

Further uses

As noted previously (CHEN 96), epitaxial diamond films have usefulness in semiconductors, where their doping with boron results in a high-speed, high-temperature characteristic useful in integrated circuits (SCHEWE 92).  Such high-bandwidth devices are in obvious demand in improving the performance of telecommunications and data processing systems integral to the information age that initiated the 21st century.  Also, as set forth in 2061, the ability to lift payloads without the conventional need for rocket propulsion or the use of chemical fuels will ultimately result in humankind's readily venturing beyond the earth and into the universe (CLARKE 87).

Carbon, as the 6th element, is central to life as it is known on the planet Earth.  Its capacity to form strong covalent bonds to itself, moreover, is the basis for the extraordinary material known as diamond, which serves life in a demonstrable variety of fabrications and uses.  Indeed, as a material it may be one of "man's best friends" as well.

(BLUENILE 03)  Diamond Cut at Blue Nile, Blue Nile, Inc., http://www.bluenile.com/diamond_cut.asp , 2003.

(CHEN 96)  Chen, Qijin et al., Epitaxially Oriented Growth of Diamond on Silicon by Hot Filament Chemical Vapor Deposition, Appl. Phys. Lett. 68 (2), http://control.uchicago.edu/~qchen/MSPapers/epitaxy.pdf , 8 January 1996.

(CLARKE 87)  Clarke, Arthur C., 2061:  Odyssey Three, Ballantine, 1987, pp. 252 - 254.  Please note Clarke's credits to Ross, 1981 and Isaacs et al., 1966.

(JAMES 03)  James, Robert, FGA, GG, Diamond, Your Gemologist, http://www.yourgemologist.com/diamond.html , 2003.

(KRANE 83)  Krane, Kenneth S., Modern Physics, Wiley, 1983, pp. 449 - 451.

(LOCKE 96)  Locke, W., Buckminsterfullerene, C60, Sussex Fullerene Group, http://www.bris.ac.uk/Depts/Chemistry/MOTM/buckyball/c60a.htm , 13 October 1996.

(PETRUCCI 82)  Petrucci, General Chemistry--Principles and Modern Applications, Third Edition, Macmillan, 1982, pp. 269 - 270.

(SARGENT 79)  Periodic Table of the Elements, Sargent-Welch Scientific Company, Catalog Number S-18806, 1979.

(SCHEWE 92)  Schewe, Philip F. et al., Diamond-Film Semiconductor, Physics News Update, American Institute of Physics, Number 97 (story #3), http://www.aip.org/enews/physnews/1992/split/pnu097-3.htm , 6 October 1992.

(VANVLACK 82)  Van Vlack, Lawrence H., Materials for Engineering:  Concepts and Applications, Addison-Wesley, 1982, pp. 393 - 397.

(WEAST 77a) Weast, Robert C., PhD, ed., CRC Handbook of Chemistry and Physics, 57th Edition, CRC Press, Inc., 1977, pp. B-13 - B-14.

(WEAST 77b) ________________________, pp. B-101.

(WINTER 03)  Winter, Mark, Carbon, WebElements (TM), the periodic table on the WWW, http://www.webelements.com/webelements/elements/text/C/key.html , 2003.