April Birthstone – Diamond

Finally! I’ve had so much going on in my life the past two months (moving, preparing for a presentation, started working again) that I have not had the time to finish and publish the April birthstone blog post. But better late than never they say so here you go!

And now this one is gonna be a goodie, I love the science behind diamonds – science that is super unique, cool and that still has scientists wondering! But I had to cut back on the info that I had originally written because I tend to be an over achiever and not know when to stop, don’t worry though, you’ll still get plenty much of fun and interesting facts about this famous gemstone!

Delicate diamond jewellery for everyday wear, made with tiny raw silvery grey diamonds and 14k gold fill, handmade by Linda Sääv Jewellery.
Diamond jewellery made with raw silvery grey 2-3mm Diamonds and 14k gold fill. Delicate birthstone jewellery for everyday wear. Handmade by me.

But first I need to be honest with you. I’ve never been that interested in diamonds, diamond jewellery that is. Particularly diamond jewellery with diamonds that fulfil all of the four C’s perfectly. But give me a diamond with a “flaw”, a rough surface, with some interesting inclusions or a more unique cut and shape, and I’ll be completely captivated and drooling over the floor!

Now, let’s start with some back story of the diamond gemstone.

The History of Diamonds

Diamonds have likely been known for as long as 6000 years and are thought to have been first discovered in India. There diamonds were found in alluvial deposits* along rivers. In the early days the diamonds were used as religious icons as well as in engraving tools due to their great hardness.

Ancient Roman and Indian Diamond Jewellery.
Ancient diamond jewellery. Left: Roman diamond ring from the 3rd-4th Century AD. Right: Indian diamond pendant necklace (www.pinsdaddy.com).

The popularity of the diamond started to rise significantly from the middle of the 19th century when diamonds where found in South Africa. Due to increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns it quickly became the most valued and popular gemstone.

                   “Diamonds are a girl’s best friend.”

                                                       “Diamonds are forever.”

Today diamonds are mainly used for two things: personal adornment and industrial use.

*Alluvial deposits are vast deposits consisting of eroded material that’s been transported by gravity and water and accumulated in the base of a mountain.

Diamond Science

A diamond is a crystallised form of carbon (C) within the cubic crystal system. It’s the hardest natural material known to man, mostly due to the strong covalent bonding between the atoms in its diamond cubic crystal structure. This type of crystal structure is made up of a repeating pattern of 8 carbon atoms that the diamond adopts as it crystallises. This pattern is really hard to explain so I will not even try to go there and just leave you with this illustration of it below instead.

Diamond Cubic Crystal System
Visualization of the diamond cubic crystal system. By Cmglee, https://commons.wikimedia.org/w/index.php?curid=28157521

If grown unhibited their crystal structure enables them to grow into perfectly shaped crystals. The most common pure shapes are: cubes, octahedrals and dodecahedrons.

Three of the most common naturally formed Diamond crystal shapes to be found: the cube, the octahedron and the dodecahedron.
Three common diamond crystal shapes found: a cube (bottom left), an octahedron (upper right) and a dodecahedron (bottom right).

What I find really awesome though is that diamond as well as graphite are both solely made up of carbon, but diamond came to be the hardest material known to man while graphite is the softest, hence its use in pencils. This big difference in hardness has all to do with in which conditions (pressure and temperature) they were individually formed, which in turn decide their crystal structure and thus their hardness.

Fun fact: at the Surface of the Earth, graphite is actually the stable form whereas a diamond is actually metastable. This means that a diamond with time could convert to graphite. But don’t worry, this conversion would probably take billions of years which means your precious diamond jewellery is safe. Unless you have eternal life. And if you do, I want to know your secret!

Fun fact II: if a diamond gets engulfed by a fire it will literally burn up and only leave a pile of ash in its place.

Diamond Sources

Diamonds are extremely rare, with concentrations of at most parts per billion in their kimberlite host rock. Before the 20th century most diamonds were found in alluvial deposits where they are found in much greater quantity. Loose diamonds are also found along existing and ancient shorelines, where they tend to accumulate because of their size and density.

Diamond in Kimberlite and Diamond in Sedimentary Alluvial Deposit
Left: a diamond in its host rock, a kimberlite. Right: a diamond in a piece of sedimentary alluvial deposit.

Where and How Diamonds Form

Most diamonds come from the Earth’s mantle, where they form deep below the surface of the Earth (about 150 – 250 km) under immense pressures and temperatures. Diamond formation is favoured by a thick lithosphere (crust + the uppermost rigid layer of the mantle) which can be found in continental areas with old (2.5 billion years old or more) stabilised crust. Such geological features are called cratons and can be found within all of Earth’s continents.

Layers of the Earth and Diamond Formation Zone
Left: the layers of the Earth. Diamonds form within the lithosphere which is the topmost two layers. Right: Cross section of the lithosphere over a craton, showing its thickness and where the diamond formation zone is.

However, there are other sources. Some blocks of the crust, or terranes, have been buried so deep as the crust thickened that they experienced ultra-high-pressure metamorphism. These terranes have evenly distributed microdiamonds that show no sign of transport by magma.

Also, when meteorites strike the ground, the shock wave can produce high enough temperatures and pressures for microdiamonds and nanodiamonds to form. These types of diamonds can be used as an indicator of ancient impact craters.

Both these last two sources produce diamonds that are way too small to be used in the jewellery industry.

Surface Distribution

Diamonds are far from evenly distributed over the Earth. Though they are almost always found in kimberlites on the oldest part of cratons which makes them easier to find. Kimberlite is a type of volcanic rock that forms at even greater depths than diamonds. As the kimberlitic magma ascends during an eruption, any diamonds within its path gets caught.

Kimberlites Around the World
World map showing the location of all kimberlites currently found.

The science behind kimberlite formation and how it ascends to the surface during an eruption is still not clear. But what scientists do know is that the whole eruption process has to be fast enough in order for diamonds to still be diamonds when they arrive at the surface of the Earth. If the eruption were to be too slow, the diamonds would have time to convert into graphite before arriving to the surface.

The Four C’s

As you may know, a diamond is graded based on the four C’s: carat, cut, colour and clarity. This method got developed in the 20th century by expert gemmologists and is based on the characteristics most important to a diamonds value.

  • Carat – a diamond’s weight, 1 ct = 200 mg
  • Cut – the quality of the cut is graded according to proportions, symmetry and polish
  • Colour – how close to white or colourless a diamond is; for coloured diamonds, how intense the hue is
  • Clarity – how free a diamond is from inclusions

Apart from the four C’s, diamonds are also cut into different shapes which all reflects the light differently, giving each shape their own unique appearance and characteristics.

Popular Diamond Shapes
Diamond shapes.

Fun fact: a large (≥100 carats or 20 g) and flawless diamond is known as a paragon and such a diamond is considered to be a perfect diamond.

Fancy Colour Diamonds

Fancy colour diamonds are a collective name given to diamonds that display a colour. The rarest and most valuable colours are saturated pinks, blues and greens. In all cases, even very slight colour differences can have a big impact on value. Other colours that falls into the ‘Fancy Colour Diamond’ category is yellow, brown, red and blue. Red and blue diamonds are extremely rare whereas brown diamonds are the most common and yellow diamonds are the second most common.

Fancy Coloured Diamonds
Fancy coloured Diamonds in a variety of cuts and shapes (www.kimberfire.com).

Salt and Pepper

As I’ve already mentioned, a diamond that fulfil the four C’s doesn’t interest me that much. They are still beautiful but for me they lack that something extra: personality. I remember when I first started seeing included diamond jewellery on Instagram (where I hang out way too much these days) and I was amazed by their uniqueness, natural beauty and character. This particular diamond, named ‘Salt and Pepper’ diamond, first appeared on the market about 10 years ago and has been inching its way up in popularity ever since.

Beautiful Salt and Pepper diamond ring and diamond earrings made by Katie Carder Fine Jewelry.
Dreamy Salt and Pepper Double Diamond Ring and Diamond Leaf Earrings by Katie Carder.

‘Salt and Pepper’ diamonds are characterized by white (salt) and black (pepper) inclusions scattered within and tend to be more silvery grey in colour rather than colourless. This type of diamond is often accompanied with a simpler type of cut such as a rose cut (my personal favourite cut btw).

Luminous and beautiful rose cut diamonds by Caleb B. Quashen.
Amazing rose cut diamonds in various shapes sold by Caleb B. Quashen.

A ‘Salt and Pepper’ diamond is not only beautiful, unusual or unique, it also shows you how beautiful flaws really can be and how they only add to their appearance.

So take it from these diamonds, flaws are BEAUTIFUL, they are a part of who you are, so let them be seen and be YOU!

Salt and Pepper Diamond Rings by Gardens of the Sun.
Beautiful Salt and Pepper Diamond Rings by Meri from Gardens of the Sun.

Now, I’d love to hear what your favourite diamond looks like. Is it colourless or coloured, clear or included, raw or faceted? Please do leave a comment below and let me know!

With ♥