The Science of Diamonds
Some Basic Priciples Behind the World’s Most Popular Gemstone
Brilliant cut diamonds are always a treat. Understanding the natural processes behind diamond formation makes these precious gemstones even more wonderful to behold.
Carbon, the Building Block of Diamonds
Diamond is an allotrope of the element carbon. Allotropes are distinct forms of the same element whose properties differ chemically and physically. Two other more familiar allotropes of carbon are charcoal and graphite (which we write with in pencils). Diamond, charcoal, and graphite are certainly distinct. Charcoal and graphite are dark, while diamond is generally colorless or light. Diamond is hard, while graphite is soft and charcoal is somewhere in between.
Although they are all the same element, their underlying structures are what sets them apart from each other. For diamond, the unpaired electrons in each carbon atom connect to other unpaired electrons to form strong covalent bonds. One carbon atom bonds to four other carbon atoms in a tetrahedral arrangement to give diamond its crystal structure.
This strong chemical bonding and solid structural arrangement allow diamond to live up to its Greek name, “adamas,” meaning “invincible.” Diamond is the hardest substance known. It also has the highest melting and boiling points. Diamond is precious enough to be a gemstone and useful enough to be used in industry and technology.
A Rainbow of Colors
Usually, when we think of diamonds we imagine a colorless stone. Diamonds come in all the colors of the rainbow: colorless, white, yellow, orange, pink, red, blue, green, gray, brown, black, and shades in between. The difference in colors depends on what other elements in addition to carbon are present in the diamond.
Specific elements are associated with specific tints. For example, if traces of nitrogen are present during formation then the diamond will have yellow or orange tones. If a stone is colorless, no other elements are present.
Inside the Earth
Extremely high temperatures and pressure far below the Earth’s surface transform reservoirs of carbon in Earth’s mantle into diamonds. Temperatures and pressures this extreme occur when tectonic plates collide. Longer exposure to high temperatures and pressure allow diamond crystals to grow larger.
Meteor impacts can also supply the necessary extreme pressure to form diamonds. Diamonds formed by meteor impact may be sprayed out from the crater along with the other impact debris.
Magmas, or molten rock, transport diamonds toward Earth’s surface along with other crystals and fragments from the surrounding mantle rock. Specifically, kimberlite and lamproite magmas are the carrying agents for diamond.
As the magmas move toward the surface, diamonds are escorted up through these kimberlite and lamproite “pipes.” Eventually, the magmas erupt and a distinct pipe shape is created. Kimberlite pipes are similar in appearance to a carrot growing in the ground while lamproite pipes are bowl-shaped.
Eventually the magmas cool off and solidify into the rock we mine to get the diamonds out of. Since surface rock erodes away, sometimes diamonds can be found in alluvial deposits in addition to diamond pipes. Alluvial deposits are sand, silt, and gravel deposited by rivers and streams. Diamonds can be transported far from the original pipes, leaving some diamonds to be found in oceans and in riverbeds.
For an easy to understand, more in-depth look at diamonds visit:
Diamonds: American Museum of Natural History
