I'll try. I assume semi-conductive refers to it's electrical properties. The tetrahedral structure of pure carbon found in diamonds is a very good electrical conductor. If impurities are introduced, that property is lessened. The neat thing, is the impurities are what give diamonds those rare and lovely colors. I believe nitrogen turns them blue and boron turns them red. All that nitrogen in Brazilian diamonds could be very lucrative, as in the Hope Diamond.
Here's some stuff from the Winspear website http://www.winspear.com/s/TechnicalOverview.asp?ReportID=859
Diamonds: Remarkable Facts
Most diamonds are at least 990,000,000 years old. Many are 3.2 billion years old.
Diamond is a crystal form of pure carbon that grows and is stable under immense pressure and heat at depths of 100-250kms beneath the earth's surface.
Diamond presents a unique assemblage of truly outstanding mechanical, thermal, electrical and optical properties:
Diamond is the hardest known mineral registering 10 on the Moh's Scale (The stable form of carbon at earth's surface, graphite, is the softest known mineral on the Moh's Scale).
Diamond is the best conductor of heat and has the highest melting point of any natural substance.
The refractive index of diamond at 2.42 is the highest of all gems. A very high dispersion, or the ability to separate white light into the colours of the spectrum, gives cut diamonds their "fire".
Diamonds are fluorescent; they emit visible light when struck by ultraviolet light.
Diamonds are triboelectic; they become electrically charged when rubbed.
A mixture of chemical impurities, temperature and pressure can effect the colour, clarity and shape of a diamond. The most valuable diamonds are colourless and flawless (no inclusions).
50 million carats of diamonds are mined every year resulting in a $5 billion/ year industry.
Retail sales of diamonds are in the region of US$40 billion; the average price paid is about $800 per piece.
Coloured Diamonds: Remarkable Facts
The cubic structure of diamond, formed of carbon, is so compact that most chromophoric atoms (colour causing elements such as iron, chromium etc.) are too large to fit its crystal lattice (structural framework).
Two kinds of impurity atoms that can act as colouring agents, nitrogen and boron, are both similar to carbon in atomic size and are thus able to penetrate a diamond's tight atomic crystal lattice and disperse through it.
Although "colourless" is ideal for a white diamond, colour in a diamond can be very valuable if it's deep enough and attractive enough.
"Fancy" coloured diamonds are extremely rare in nature and comprise only 1-2 carats of coloured gems out of every 3,000 carats of gem-quality that are mined.
The highest auction price ever paid for a coloured diamond was US$926,315 per carat for a 0.95 carat, cut and polished purplish-red diamond in 1987. As of the close of 1991, "fancy-coloured diamonds" held the top 19 per carat auction price records at values that ranged from $926,315 to $207,174 per carat.
To compare, the world record price for a colourless diamond was US$142,232 per carat paid for a 52.59-carat rectangular cut gemstone in 1988. |
