Walk into any jewelry store, and ask to see a diamond with eye-visible black spots. Ask the salesperson what the spots are, and he or she is likely to tell you that they are "carbon spots," or bits of carbon, the element that makes up a diamond, that were not dissolved when the diamond was formed. Mother Nature was boiling up some carbon to form diamonds, and some of the carbon just didn't become a diamond. It makes sense, right? Wrong (well, mostly wrong).
Diamonds can have inclusions of graphite, which is carbon that formed with a different atomic structure than a diamond. Graphite is usually a dark gray color and can definitely appear black in various lighting conditions. But not all inclusions are created equal. There are many different possibilities as to what a particular inclusion can actually be. The only quick answer is that dark inclusions are included crystals (xenocrysts) that may actually be a very dark-toned red, green, brown, etc. The only way to know for sure is to have an advanced gemological laboratory use sophisticated equipment to analyze the chemical make-up of the inclusion.
The moral of the story is this: if you are being sold a diamond that has "carbon spots," I recommend that you run away - far, far away - and find a more knowledgeable jeweler or gemologist. And trust me, you do not need to dip into the I-clarity range to find a diamond that maximizes your diamond budget.
Originally posted by me to LibertyDiamonds.com on 4/6/2010.