Cochise College                Student Papers in Geology     
Geology Home Page                          physical geology  historical geology  planetary  gems                        

Roger Weller, geology instructor                     

Diamonds and Pearls
Erin E. Unger
Physical Geology
Spring 2009


       Just Icing On The Cake

 Tiffany & Co., or Blue Nile are the jeweler’s that flash through the mind when a set of exquisite tear drop pearl earrings is seen gracefully dangling from a ladies ear; or when a diamond engagement ring captures the eye with its shining beauty. Both diamonds and pearls are made into beautiful pieces of jewelry although how each gem is created, the set or mount in different pieces of jewelry and the care of the gems once set, is as different as a diamond is from a pearl.   


     The carbon that makes diamonds comes from the melting of pre-existing rocks in the Earth's upper mantle, or crust. There is an abundance of carbon atoms in the mantle. Temperature changes in the upper mantle forces the carbon atoms to go deeper where it melts and finally becomes new rock, when the temperature reduces. If other conditions like pressure and chemistry is right then the carbon atoms in the melting crustal rock bond to build diamond crystals, thus diamond deposits. Of all the diamonds mined in the world each year, less than half are gem quality. Gem quality diamonds are the diamonds used in jewelry. The clarity of these diamonds ranges from flawless to inclusions and flaws visible to the naked eye.

     The harvesting of diamonds is done through pipe mining. Pipe mining refers to the extraction of diamonds from volcanic pipes. In most countries, a diamond pipe mine is composed of kimberlite, or blue ground. After the diamond-bearing rock is brought to the surface, it is then transported to a screening plant where the diamonds are separated from the host rock.

     Diamond cutting and polishing requires several hours or several months to complete. The rough diamond is divided into two parts by sawing or cleaving. Most stones are sawn across the "grain" (visible evidence of the diamond's crystal structure). Once the polishing of the diamond begins; one by one, facets will be ground on to the stone. Most diamond cuts have 58 facets. A well-cut diamond will be fiery, brilliant and beautiful. A well cut and polished diamond will be one of these three cuts; the round cut, the princess cut, or the emerald cut.

     To clean diamond jewelry, it is best to use an ammonia water mixture, and gently scrub the jewel’s surface with a tooth brush. Also storing these pieces separately from other jewelry will protect it from being scratched or chipped. Each glittering stone can be set in many different ways to make many different items including; engagement rings, necklaces, pendants, bracelets, earrings and watches.  

     Most of today’s pearls are cultured instead of being harvested naturally. Pearls are formed by an oyster’s reaction to an irritant getting inside of it. Over a long period of time an oyster will cover the irritant with many layers of a substance called nacre to protect itself. This process of layering the grain of sand with nacre results in a beautiful lustrous pearl. There are many different kinds of pearls each one being a different color, shape, or type. The color of a pearl can be white, white rose, black, silver, gold and pink. Pearls can be round, off-round, oval, teardrop, and semi- baroque. The types of pearls include;   freshwater, akoya, south sea, and Tahitian. To harvest pearls workers have to pry open oysters, and separate the two shell valves, by cutting the adductor muscle, making an incision on the gonad and squeezing the pearl out. Machines used for pearl extraction go about this process by dissolving the oyster soft body parts with the use of chemicals while the pearls remain as they are and become easily extractable. Once the pearls are harvested they are washed in distilled water, polished with refined salt and sorted for sale according to size, color, shape, and luster. The care and maintenance of pearl jewelry is an easy task. Simply by wearing the jewelry, the natural oils in the skin keeps pearls lustrous, so the more often they are worn, the more beautiful they will look. Along with wearing them, they should be wiped off with a soft cloth after each time they are worn. Pearls can be set and mounted in any manner, just like diamonds can be. A quality string of pearls is recognized by a knot placed between each pearl on the string so that one pearl is not rubbing against the one next to it.


     All diamond and pearl jewelry creations are of stunning elegance and captivating originality, they are designs that bring glamour to life and will be cherished always. Bracelets can range from grandeur, to simple elegance. Necklaces and pendants are poetry in motion, captivating all as they proclaim one’s personal style, and taste. So with this thought in mind, we can make the determination that both diamonds and pearls are extraordinary works of art, from the beginning formation of each, all the way through to the display cases in jewelry stores around the world.


Works Cited

Photo credits