Inclusions found in Diamonds tell quite a Tale

A flaw seen near the center of a diamond crystal - Wikipedia

The inclusions found in a natural diamond are a window on the interior of the earth.  Basically there are two types of inclusions found in a diamond.  The first type is a Syngenetic inclusion that was formed in the natural process of crystallization was ongoing.  The second type is the Epigenetic inclusion that was formed after the diamond was made.

The most serious flaw is a cleavage that can compromise the stability of a diamond.  These cleavage cracks are straight.  If they are serious enough they can split a diamond along the cleavage crack.  The diamond cutter often takes advantage of this flaw to cleave a diamond into two or more pieces.  They will also cause a diamond to split if accidentally subjected to a sudden high pressure event.

Bearding is hair-like cracks that often happen during the cutting of a diamond usually occurring around the girdle.  This is the area in the Anatomy of a Diamond where the setting prongs grasp the diamond.  Sometimes this flaw is also called “girdle fringes.”

Growth lines are sometimes called grain lines they typically form while the diamond crystal is growing.  If irregular crystallization occurs this is often a reason why these lines form.  If they are colorless they don’t affect the diamond’s clarity.  Sometimes though they are white or colored they are more visible and do affect the value of the diamond.

The next group of inclusions is man made that called ‘laser lines’ and can come from several different operations on the diamond.  The most common type is where the diamond cutter has used a laser for removing dark or prominent inclusions from the diamond.  The second most common is from the use of a microprobe used to analyze the tiny crystals of other minerals that are Syngenetic inclusions in the diamond. 

Feathers derive their name because they actually look like small feathers inside a diamond.  These seem to be Syngenetic tiny cracks that formed with the diamond.  Small feathers seem to be harmless, but if they reach the surface of the diamond crystal then can increase the risk of breakage. 

The last group of inclusions is definitely Syngenetic in nature; they are called pinpoints.  These are crystals of other minerals that were trapped inside the diamond crystal as it formed.  These are true windows into the interior of the earth as they were formed billions of years ago.  These same crystals are used by geochemists using a microprobe to determine their composition, and learn about the interior of the earth.  The most common inclusions are pyrope garnet, pyrite, zircon, eclogite and other rare minerals.  Sometimes an inclusion inside a diamond is what is termed a negative crystal which is just a void looking like a diamond crystal.  Other inclusions are minute drops of liquid usually water or liquid carbon dioxide.

Flaws are the characteristic inclusions found in a diamond.  They are called flaws because their presence means that the diamond is not perfect.  These inclusions act like fingerprints because no two of them are the same they are used to identify individual diamonds if they are lost or stolen.  Other inclusions affect a diamond’s clarity causing it to be less brilliant as they interfere with the light as it passes through a diamond.  There are other inclusions that can cause a diamond to fracture if it is subjected to a sudden sharp blow.

References:

Mineralogical Association of Canada, Editor Lee A. Groat, Geology Of Gem Deposits, Short Course Series, Volume 37, Yukon Geological Survey, © 2007, Yellowknife, Northwest Territories
Gem Deposits, http://amonline.net.au/geoscience/earth/gem.htm
Geology of Gem Deposits, Mineralogical Association of Canada, Editor Lee A. Groat, http://www.mineralogicalassociation.ca/doc/promo_SC37.pdf  Volume 37 © 2007
Industrial Minerals and Rocks, Page 418, http://books.google.com/books?id=zNicdkuulE4C&pg=PA417&lpg=PA417&dq=kimberlites+and+the+occurance+of+diamonds&source=bl&ots=Nhqev_Ebqc&sig=WQyRiIxdpBMtnaZWwhGwKC5o1sY&hl=en&ei=csyvSbDZAojWnQfAmpTNBQ&sa=X&oi=book_result&resnum=9&ct=result#PPA418,M1

Kimberlite, Wikipedia the free encyclopedia, http://en.wikipedia.org/wiki/Kimberlite

Diamond Inclusions, http://jewelry.about.com/cs/diamondclarity/a/inclusions.htm