Where in the world do I start on talking about diamonds? How in the world can I even begin to describe the glories of a gemstone composed of carbon?
That’s right, diamonds are made of carbon. The carbon atoms are processed in minerals where carbon is always present. It appears that the best way to start talking about diamonds is where and how diamonds form deep in the earth, like this diamond encased in kimberlite, which we will talk about soon.
Diamonds, the symbol of everlasting romance, need to endure extraordinary temperatures and tremendous amounts of pressure to become the beautiful and sparkling gem we all know and love today. Between 2.5 billion to 20 million years ago, diamonds formed 90 to 120 miles beneath our feet in stable areas called cratons. Cratons are the oldest and most stable land masses on the planet.
In order for the carbon to form into a diamond, the temperature range has to be between 1652°F to 2372°F and the pressure has to be between 45 kilobars and 60 kilobars. A kilobar is a unit that scientists use to measure high pressure. So 45 to 60 kilobars is really 45,000 to 60,000 times the amount of normal pressure on the earth’s surface at sea level. This makes diamonds a true symbol of endurance.
The minerals that can endure the extreme heat and pressure to form diamonds are called peridotite and eclogite, where carbon is always present. Peridotite is one of oldest rocks in existence and carbon is released from the peridotite as it melts from the earth’s inner heat. The carbon’s release is consistent and always present, therefore diamonds are forming even as you read this delightful article. Peridotite is on the left and eclogite in on the right. These pictures are from the Smithsonian website.
Eclogite is younger than peridotite and occurs at shallower levels in the earth’s mantle. The carbon in eclogite mostly comes from organic compounds that existed millions of years ago. The organic compounds become part of the eclogite and the resulting carbon gets released when subduction occurs. Subduction is when two plates on the earth’s crust collide, forcing one under the other.
After crystallizing, t
he diamonds travel to the surface while still under incredibly high pressure and high temperatures in kimberlite and lamproite pipes at speeds over 186 miles per hour. Kimberlite and lamproite are minerals that transport the diamond crystals to the earth’s surface in a few hours. After traveling through the kimberlite and lamproite pipes, the diamonds enter the earth’s surface through volcanic explosions! High-quality diamond rough usually form into lovely octahedrons - double sided pyramids.
During that time, if the pressure decreases while the heat remains the same, the diamond will transform into graphite. Depending on the conditions, you’ll either get a ring or a pencil. On the left is a piece of graphite and its atomic structure from my photo collection and on the left is the ideal atomic structure for a diamond, which is an image I found on the GIA website.