Diamond, From ash and slime to indestructible beauty.

Natural diamond in all its glory.

Times are stressful this spring, but as a silver lining that just allows us more time to stop and smell the spring flowers, I hope. Maybe this post can help distract you for a minute or two as we talk about something more… adamant… say a diamond?  

Like my pun? 

Here’s a fun fact, ‘adamant’ derives from that same Greek roots as the root word for diamond, “a” and “daman” which means “not” and “to tame”. Diamonds are the traditional birthstones of April and are the hardest natural materials known to man, hence they could never be tamed, until now. Their hardness is what made it difficult to use in jewellery prior to the turn of the century and thus kept it out of main fashion lines till the Industrial revolution.  

There are several reasons why a diamond is so hard. First, what is a diamond? 

Diamond is identified as:

  1. Cubic Crystal System (graphite is Hexagonal)
  2. Native Element (a pure element in natures found chemically ‘unbound’ with another element, like gold)
  3. Mineral = Diamond – C

Now there are varieties of diamonds called “fancy diamonds”, these are coloured diamonds as opposed to the original white/colourless we usually see. They can come in all the colours, with red and pink being the rarest colour and yellow being more common. There are also green, blue, orange, violet, chocolate and black varieties.   

The many colours of fancy diamonds: green, yellow, orange, red, pink, violet and blue.

Diamonds are actually a metastable, crystalline form of pure carbon. They are polymorphs of graphite, meaning the “lead” in your pencil and that engagement ring on your finder have the EXACT same chemical composition, just different crystal structures. The difference is how the atoms have arranged themselves. In graphite the carbon forms sheets that are weakly bound together, hence graphite is used as a lubricant in certain machinery, the atomic sheets just slide by each other. In diamond, the carbon atoms are arranged into tetrahedrons, triangular pyramids. This is what gives the diamond it’s strength, as pyramid after pyramid is stacked together, like trusses of a bridge, growing in all directions equally. 

The atomic structure of diamond and graphite displaying how carbon orients itself.

Interestingly, while diamonds are the hardest, they are not the toughest; Diamond & Diamond Lawyers didn’t do their research. First we need to establish the difference in terminology. Hardness, it the measure of resistance to scratching/indentation. Toughness is the resistance to withstand mechanical shock. Due to the tetrahedral structure of diamond, there are weak points, known as cleavage, that follow aligned atomic bonds. This makes diamond brittle, not fragile, but if you apply the right amount of force at the right angle you will cleave a diamond. This was how we originally cut diamond, by breaking it along cleavage plans using other diamonds and metals tools to create very crudely, unappealing, basic gemstones cuts. To top off this little factoid, jade is actually tougher gemstones than diamonds as they are composed of softer microcrystals that are interlocked/woven with each other. They don’t have a cleavage point thus resist impact better than diamond. Diamond lawyers should be saying there’s nothing HARDER than a diamond, but that’s no longer the case too. I’ll talk about that another time. 

Just how hard is a diamond? well is almost 4 times as hard as sapphire (corundum). Vickers hardness tests how much pressure it takes to make an indentation with another diamond into the surface.

Now for these crystals to form we need to go deep into the earth. For scale, the deepest mines are about 4km deep in South Africa and the deepest humans could ever drill was 12,262 metres (40,230 ft), in Russia. Diamonds form 150-200km below the surface of the Earth, and that’s not even deep on the Earth’s scale. Here, temperatures average 900 to 1,300 degrees Celsius and at a pressure of 45 to 60 kilobars (which is around 50,000 times that of atmospheric pressure at the Earth’s surface)! You find this kind of high pressure and low temperature (relative to the rest of the mantle at that depth) at the base of the continents, also known as a cratonic root. Cratons are ancient continents dating well over 4 billion years old, they are the first continents are formed long ago on the early earth and are characterized as the stable sections of a continent (no major earthquakes or volcanoes). The Canadian Shield you see up in cottage country north of us is such a craton, hence we have found diamonds in Canada. Now, ready for a little science that’s almost fiction? 

Geologists and chemists are able to analyst the inclusions in diamonds to help identify depth and pressure. See some of those inclusions in your ring, that people find undesirable, could actually be deep earth minerals Minerals that are only stable under extreme pressure and temperatures and would never be found on the earth’s surface. They are also able to analyze the stable isotope ratio of the carbon within a diamond, as in how much C12 there is to C13. Looking at this ratio, geologists discovered some diamonds carry ratios that are similar to modern life, algae. Life prefers to use C12 over C13, so it’s possible the diamond came from organic material or ancient algae and cyanobacteria slime that was pushed back deep into the earth along subduction zones (think Marianas Trench, like the band). That’s right, you could be wearing ancient crystalline slime dusted with rare minerals from deep within the Earth.    

Garnet inclusion within a diamond. This garnet while similar to surface garnets could very likely be a deep earth garnet, and only able to survive on the surface environment because it’s sealed within.

Another really cool interesting fact is how diamonds came to the surface. As we discussed above, diamonds need lower heat and extreme pressure from deep below the surface. If they are brought up too slowly, diamonds will transform into graphite as this structure is more stable on the Earth’s surface environment. Therefore, the diamonds we are mining today had to be brought up rapidly, so fast, in fact, they have evidence of these eruptions breaking sonic speeds. These eruptions are known as diatremes or maars

A simple diagram of a diatreme, magma forces itself along fractures and weak points in the crust thus forming dykes. When the pressure is released, a cone (like a carrot) is formed. Xenoliths are the pieces of deep crust brought up from the violent eruption, this is where the diamonds reside.

Diatremes are the result of deep magma plumes pushing to the surface and then violently reaching with groundwater to produce an eruption. This explosion is like popping a champagne cork as the released pressure allows all the built-up pressure from below to explode out. As the magma from below erupts it fractures, pulls and drags the surrounding rock to the surface. This magma produces a rock known as lamproites. If your magma happened to source below and flow through the old cratonic roots as we discussed above, there is a chance these deep eruptions can carry diamonds, creating the ore known as kimberlite, diamond-bearing lamproites. 

Kimberlite ore with a diamond in the rough.

Next time when you are showing off your diamond, and your friend points out a little black spot, let them know what that little black spot really is. 

Stay tuned for next month as we discuss jump back into beryls; the emeralds of May.