How many people have died so that your diamond could live forever?
• The first recorded history of the diamond dates back some 3,000 years to India
• Decorative, brilliance, and probably rarity
• Many myths
• At one time ingested in the hope of curing sickness
• During the Middle Ages – diamonds gained monetary value – mine owners perpetuated myths that diamonds were poisonous – to prevent the mineworkers swallowing the diamonds in attempt to smuggle them out of the mines
What are diamonds?
• Carbon, same as graphite – what we use in pencils
• Has amazing properties – will see how these affect uses
• Probably most famous for it’s hardness:
• Hardest substance on earth, 10 on Mohs
• Exponentially harder than corundum (from which rubies and sapphires are formed) which is 9
• It is difficult to measure hardness (scratch)- diamond must be used to measure its own hardness
• To abrade a diamond – use another diamond to abrade diamond along its softer directions by the action of its harder directions – direction parallel to the crystal axes are those of least hardness.
• Hardest diamonds in the world – from the New South Wales, Australia – also used to polish other diamonds.
• “hardest substance on earth” is now also a myth: Physicists – Germany have created a material that is harder than diamond – made the new material by subjecting carbon-60 molecules to immense pressures – new form of carbon known as aggregated diamond nanorods
• Despite hardness- are not unbreakable: A diamond’s crystal structure has “hard” and “soft” directions. A blow of sufficient force, in a very exact direction, can crack, chip, split or even shatter a diamond – which is how they cut diamonds
• Other properties:
• least compressible substance
• stiffest substance
• extremely low thermal expansion
• inert with respect to most acids and alkalis
• is one of only a few materials with a negative electron affinity – as result will repel water (unusual property for a mineral) but will readily accept wax and grease
• is transparent from the far infrared through the deep ultraviolet
• highest index of reflectance and refraction of any transparent substance = light-bending ability -able to throw back almost all the light that enters a well cut gem
• exhibits strong dispersion = ability to separate the various colors of the spectrum – causes the gem to throw back the bright flashes of separated colors (“fire”)
• many diamonds glow in the dark:
o when illuminated by ultraviolet light, certain diamonds can absorb the high-energy radiation and re-emit it as visible light (blue to violet) = fluorescent
o some of those even continue glowing (yellow) after the ultraviolet source is turned off = phosphorescent
• Diamonds occur in every color of the rainbow – cause lies at atomic level
• In pure diamond visible light does not possess enough energy to excite electrons in the bonds and consequently no light is absorbed in the visible band and all the light falling on the diamond is transmitted and refracted back to the eye causing the diamond to appear completely colourless.
• However, most diamonds are not perfect. The diamond lattice contains impurities such as nitrogen and the lattice is sometimes defective with a missing atom
o Yellow: Nitrogen is the cause of colour in these diamonds.
Brown: Plastic deformation of the diamond lattice whilst in the earth.
Pink & Mauve: Plastic deformation of the diamond lattice in the upper mantle region of the earth.
Black: Caused by a vast quantity of dark opaque inclusions.
Blue: Boron impurity in the lattice.
Green: Caused by alpha particle radiation.
• The rarest colors are red and purple, and combinations of those two colors.
• Yellow and brown are the most common color of diamond
• Colorless is the most popular as far as jewelry is concerned
• Blues and greens are very rare, especially naturally colored stones
• Some lightly colored diamonds (light light pink, light light blue, etc.) are irradiated to make their color more intense – darkening the outer part of the stone all the way around – process is permanent and professionally accepted in the diamond industry
• Most exciting properties:
• ability to be a semiconductor when doped with boron
• exceptional thermal conductor – 4 times better than copper
• called “ice” with good reason. Objects feel cold not only because they are at a lower temperature than our bodies, but also because they can extract or conduct the heat away from us. When you touch a diamond to your lips, it feels ice-cold because it robs your lips of their heat.
What are diamonds used for:
• Aside from making a few people very very rich and financing wars …
• 25% of mined diamonds used in jewellery – based on optical properties
• Diamond is the most important gemstone in the industry – 80 % of the gem trade
• Only 20 percent of mined diamonds are used in jewelry
• An average of 250 tonnes of ore must be mined in order to produce a one-carat gem quality polished diamond
• 4 c’s used to determine the relative value of a diamond”
• Cut – brilliant is best for revealing optical properties
• Clarity – when diamonds have inclusions they loose some of their refractive property making them less brilliant
• Colour – degree of transparency of a diamond – graded from a scale of D (colorless) to Z. The clear diamonds are the most popular
• Carat – comes from the carob seed – used as a measure in ancient India because it was small and consistent in weight. A carat weighs 1/142nd of an ounce. That is, 142 carats = 1 ounce.
• Special diamonds like:
• The Cullinan Diamond – South Africa – 1905 – 1.5 lbs – 3,106 carats – took 3 months just to decide how to cut it, what shapes to give the finished gems in order to maximize yield from the rough – yielded 9 major stones, 96 brilliant cut diamonds, and 9.50 carats of unpolished pieces – 65% lost as part of cutting process
• Re Life Gem: The remains of one person typically yield a diamond between .25 carats and 1.3 carats – insurance issues!
• 75% of mined diamonds used in industry
• Abrasives and cutting tools
• cut much faster and accurately than other tools – metals can be sliced thinner than human hair by the diamond blade – take advantage of hardness properties
• Diamond-studded rotary bits are used to drill oil wells and bore tunnels in solid rock
• Glass cutters
• Low-grade diamond crushed to dust
• sorted by grain size through special sieves
• used as abrasive powder – e.g. to cut and polish gems
• powder is either sintered into metal disks, formed in carbide grinding wheels, pressed into metal, or mixed in an oil paste
• Very thin wire formed by pulling thick wire through a graduated series of diamonds with tiny holes drilled through them
• Although used to cut, grind, and polish many materials, diamonds aren’t used to machine alloys of iron because the diamond abrades very quickly, due to a high-temperature reaction between iron and carbon
• Mechanical parts that must resist wear, undergo a sudden temperature changes and that must not change size, create friction or rust
• No friction is created when rubbing them together – Some machines turn at 90 000 revolutions a minute – no lubrications are needed to keep the bearing from wearing away
• Diamond anvils
• E.g. expose microbe samples to pressures 16,000 times greater than typical sea-level pressure – similar to pressures that exist about 50 kilometers under the Earth’s crust – about 1% survived under these conditions for 30 hours – suggested might also be able to withstand the sort of high-pressure environments found in the Earth’s deep subduction zones or on Jupiter’s moons Europa, Callisto and Ganymede
• Future uses – have been too expensive up until now but … – market for industrial diamond is growing at 10% to 15% per annum
• molecular structure – ideal for handling high voltages – switches for big municipal power grids
• lasers of extreme power
• biological sensors – one day be implanted in the human body – resist corrosion
• frictionless medical replacement joints
• coatings that could withstand extreme heat and would never scratch or wear out
• windows on spacecraft as they leave and re-enter Earth’s atmosphere
• a wear-resistant coating for military equipment -withstand the searing heat of more sophisticated lasers
• high thermal conductivity (ice) – to extract heat from electronic devices or coat integrated circuits so don’t have to cool components individually – allowing them to be smaller and more powerful – at speeds that would melt innards of today’s computers (consider heat of a laptop)
• cellphones could fit in watches – iPods could store 10,000 movies not just 10,000 songs
• What makes future uses possible … related to how diamonds are formed …
How are diamonds formed?
• Natural diamond likely the oldest thing you will ever own – two thirds the age of the Earth
• Formed on Earth approx.3 billion years ago – 150 km beneath the earth’s surface – very high temperatures (between 900 and 1300 degrees Celsius) and great pressure
• Most delivered to surface by explosive, gas-rich magmas rising at speeds up to several 100’s km per hour – up through pipe-like structures = pipes
• Kimberlite = rock formed by this magma
• If magma happens to encounter diamonds at depth – carries diamonds with it to surface = diamondiferous kimberlite – Only one in 5 pipes is diamondiferous – only 1% of pipes worldwide are economic
• The geographical distribution of kimberlites is not random – are located in the oldest parts of the continents – Archean cratons – rocks older that 2.5 billion years
• Kimberlites occur in clusters of several pipes – pipes in a cluster are typically at most tens of kilometres apart
• Some diamonds incorporated in rocks during great collisions and upheaval of continental plates
• Tiny, powder-sized diamonds also formed by shock waves from explosions – e.g. impact diamonds formed by meteorite bombardment
• Others formed in space by same way – impact = solar diamonds
• Synthetic diamonds – produced since 1950’s by high temperature (1400 C)/pressure (55,000 atmospheres) techniques and shock wave techniques to change graphite into diamond – but only tiny, powder-sized diamonds could be produced
• Today 100 metric tons synthetic diamonds produced annually
• 2 methods to produce synthetic diamond:
1. High Pressure High Temperature Synthesis (HPHT)
• graphite + metallic catalyst placed in a hydraulic press under high temperatures and pressures
• Over the period of a few hours the graphite converts to diamond
• few millimeters in size – too flawed for use as gemstones – extremely useful as edges on cutting tools and drill-bits and for being compressed to generate very high pressures
• so routine that thousands of small plants all over China pour out synthetic diamonds suitable for cutting stone
• Gem-quality diamonds of one carat or more, however, are trickier because at that size it’s difficult to consistently produce diamonds of high quality, even in the controlled environment of a lab
2. Chemical Vapor Deposition (CVD) –diamond’s future potential lies in this process
• Produces Thin Film Diamonds
• low-pressure, high-temperature method – uses heat energy from plasma and a combination of gases to rain carbon atoms on a starter seed of the gem, which gradually grows into a larger single-crystal diamond
• produces a more uniform, consistent diamond in sizes large enough to make an effective transistor
Where are diamonds found? (See Atlas of Canada)
• Top diamond producing countries: Australia (Argyle = world’s largest mine; only 5% gem quality), various African countries (Botswana, Congo Republic, South Africa), Canada, Russia
• In 2005, Canada produced 12 million carats of diamonds with a value of $1.663 Billion CDN
• 3? operational mines in Canada, the Diavik, Ekati, Jericho, Snap Lake (Attawapiskat; DeBeers) mine
• Canada is 3rd largest diamond producer in terms of value – 6th in terms of volume – sector in early development
• We have good kimberlite!
• Kimberlite normally yields an average of 1 carat (equivalent to one-fifth of a gram) per metric ton of rock – one of the Diavik mine pipes yields an average of 4.8 carats per ton, a large proportion of which are high quality gems, and is thought to be the richest pipe in the world
• The ratio of diamond-producing kimberlites is also much higher in Canada
o It has been reported that 3.1 % of the 540 kimberlites found in Canada prior to 2003 were worth mining
o By comparison, only 0.7 % of the 6395 kimberlites found across the globe were worth mining
o That means Canadian mines are four times more likely to be successful
• Lots of potential in Saskatchewan:
• One of the largest known kimberlite clusters in the world
• Recall, on average, 20% of kimberlite pipes are diamondiferous – 80% of Saskatchewans’ kimberlite pipes are diamondiferous
• 130 of the 2000 kimberlite pipes known worldwide are macro-diamond bearing. 23 of these are located in Saskatchewan.
• Canada is forecasted to become the most important diamond-producing country in the world over the next twenty years
• Canada has a lot of diamond potential, we were just slow to the starting gate
• Recall placer deposits – diamonds usually found by following trail of diamonds eroded and transported away from kimberlite pipe by rivers – but glaciers confused the issue – advancing glaciers have dispersed the material that was eroded before and during the glaciation during the Ice Age
• Wasn’t until 1980’s that 2 B.C. prospectors finally found diamonds in the NWT – sparked largest staking rush in the world – exploration crews threw wooden stakes bearing claim tags from helicopters so as to not waste time landing
• critical areas of discovery: Nunavut, Quebec, Saskatchewan, Northwest Territories and Ontario
• Canada also important because along with Australia broke the DeBeers cartel – produce diamonds out of DeBeers control
• Canada’s nature as a country has changed the world of diamonds – we produce clean diamonds in a lawful country; modern and democratic
• NWT First gov’t in the world to brand it’s diamonds – laser-inscribed and with certificates of authenticity
• And now have lured in some of world’s largest cutting and polishing firms into the country so that diamonds don’t have to be transported (and possibly mixed/exchanged for blood diamonds)
How are diamonds mined and processed?
• Hard rock
• Open pit or underground
• The host rocks are crushed – diamonds are separated from the lighter minerals by gravimetric methods such as rotating pans – produces a heavy mineral concentrate
• One of two things is done with the concentrate:
• blended with water and passed over a sloping table covered with a mixture of wax and grease – “grease table” – diamonds stick to the table, while the wetted waste minerals wash over it ; or
• passed in a dry state through an x-ray sorting machine – Diamonds fluoresce when exposed to x-rays – Sensors detect the flashes of light emitted by the diamonds – sends a signal to the microprocessor that fires an air blaster valve at the appropriate moment, blowing the diamonds into a collection box
• Alluvial, placer, marine deposits
• Where has been eroded from pipe and deposited away from source – river gravels, beach terraces, off-shore marine deposits
• May be mechanized, often human labour = artisanal mining, literally digging and sifting through deposits
• Alluvial or “artisanal” diamond mining from secondary-deposits still accounts for 90% of West Africa’s diamond exports – Sierra Leone’s second largest ’employer’ after subsistence
Beyond the mine:
• Weighed and valued by the mining company and the gov’t
• Then all diamonds are shipped to Antwerp or London where they are appraised and valued
• Once a month there is a sale or a ‘sight’ – buyer presented with a parcel of uncut stones and must either purchase or reject the entire package without choosing among the various stones
• Then on to India, Israel, New York or London to be cut
• ? appraising and cutting now done in Canada ?
• Cutting and polishing takes several hours to several months to complete – during which diamond loses on average, half of original weight
• Diamonds will be either cut or cleaved to size using a paper-thin metal disc coated with diamond dust or a laser, or split along the grain by a single blow from a steel blade
• Next, 58 facets are ground and polished onto the stone – and they have to be done so in correct proportion so that 1/3 of the total weight is above the girdle and 2/3rds is below – and that light reflects perfectly
• Then set
Issues surrounding diamonds:
• Conflict or blood diamonds
• DeBeers cartel
• Child labour
• Health and welfare of diamond miners/cutters
• Environmental impact of mines
• Aboriginal land claims and diamond mines