Properties of Diamonds<

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.

Hardness and Crystal Structure of Diamonds

Diamonds (also known as adamant) are the hardest known naturally occurring material, scoring 10 on the old Mohs hardness scale. 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. The diamond derives its name from the Greek adamas, which means "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 of diamond properties 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.

Optical Properties of Diamonds

The lustre of a diamond is described as adamantine, which simply means diamond-like. Diamonds exhibit fluorescence of various colors under long wave ultra-violet light, but generally bluish-white, yellowish or greenish fluorescence under X-rays. 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.

Electrical Properties of Diamonds

Except for most natural blue diamonds which are semiconductors, diamond is a good electrical insulator, but unlike most insulators, is a good conductor of heat because of the strong bonding within the molecule. Specially purified artificial diamonds have the highest thermal conductivity (20-25 W/cmK, five times more than copper) of any known solid at room temperature. Most natural blue diamonds contain boron atoms which replace carbon atoms in the crystal matrix, and also have high thermal conductance. 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.

Thermal Properties of Diamonds

Because diamonds have such high thermal conductance they are already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating. 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).

Clarity of Diamonds

Clarity is a measure of internal structural imperfections called "inclusions". Grades of clarity, which are mostly those used by Gemological Institute of America (GIA), are:

All grades reflect the appearance to an experienced grader when viewed from above at 10x magnification, though higher magnifications and viewing from other angles are used during the grading process. In "colorless" diamonds, dark inclusions will tend to create the greatest drop of clarity grade. In other colors pale inclusions may have greater relief (may stand out more) and may cause a greater drop in grade.

Beyond the clarity grading terms, other considerations include the type, size and location of the "inclusion". Inclusions near or on the surface may weaken the diamond structurally. Depending on where the inclusion occurs in the cut diamond and how it is to be used, it may be possible to hide the inclusion behind the setting.

Laser "drilling" involves using a laser to burn a hole to a colored inclusion, followed by acid washing to remove the coloring agent. The clarity grade is the grade after the treatment. The treatment is considered permanent and both the GIA and AGS will issue grades for laser drilled diamonds. Reputable vendors should disclose that laser drilling has been used.

Clarity can also be "enhanced" by filling the fracture much like a car windshield crack can be treated. Such diamonds are sometimes called "fracture filled diamonds". Reputable diamond dealers must disclose this filling and reputable filling companies use filling agents which show a flash of pale color, commonly pink, when viewed closely. There is a significant price discount for fracture-filled diamonds. The GIA will not grade fracture-filled diamonds, in part because the treatment isn't as permanent as diamond. Reputable companies often provide for repeat treatments if heat causes damage to the filling. The heat required to cause damage is that of a blowtorch used to work on settings, and it is essential to inform anyone working on a setting if the diamond is fracture-filled, so they can apply cooling agents to the diamond and use greater care while working on it.

Color of Diamonds

The Gemological Institute of America uses as "D" to "Z" scale for color where "D" is colorless and "Z" is yellow:

Colourless diamonds are priced higher than yellow diamonds. Diamonds of other colours may be priced higher than yellow diamonds and are graded "Z+". Fancy-coloured diamonds such as the deep blue Hope Diamond are particularly valuable. Brown rather than yellow as the colour became more common as Australian diamonds entered the market and is generally less appreciated by consumers and sold at a greater discount if the colour is readily visible.

80% of the diamonds produced are poorer quality (discolored, less transparent) diamonds which are used as industrial diamonds, where their extreme hardness is useful in cutting and grinding otherwise intractable materials (including other diamonds). Lately, gas-phase deposition processes have been devised that allow thin diamond films to be grown on some surfaces, greatly increasing the durability of some machine tools.

While the prices are higher for colourless diamonds, the exact colour most valued by a consumer is a matter of personal preference, with some preferring the very transparent D-F range, while others prefer the "warmer" colours in the G-J range and still others prefer a clearly visible tint.

Said the old priest, ``A diamond is a congealed drop of sunlight.'' Now that is literally scientifically true, that a diamond is an actual deposit of carbon from the sun. The old priest told Ali Hafed that if he had one diamond the size of his thumb he could purchase the county, and if he had a mine of diamonds he could place his children upon thrones through the influence of their great wealth.

Ali Hafed heard all about diamonds, how much they were worth, and went to his bed that night a poor man. He had not lost anything, but he was poor because he was discontented, and discontented because he feared he was poor. He said, ``I want a mine of diamonds,'' and he lay awake all night.

Early in the morning he sought out the priest. I know by experience that a priest is very cross when awakened early in the morning, and when he shook that old priest out of his dreams, Ali Hafed said to him:

``Will you tell me where I can find diamonds?''

``Diamonds! What do you want with diamonds?'' ``Why, I wish to be immensely rich.'' ``Well, then, go along and find them. That is all you have to do; go and find them, and then you have them.'' ``But I don't know where to go.'' ``Well, if you will find a river that runs through white sands, between high mountains, in those white sands you will always find diamonds.'' ``I don't believe there is any such river.'' ``Oh yes, there are plenty of them. All you have to do is to go and find them, and then you have them.'' Said Ali Hafed, ``I will go.''

-- from Acres of Diamonds by Russell H. Conwell