Birthstone Spotlight: August Peridot

peridot-august-birthstonePeridot is one of my favorite gems, not only for its beauty, but because there are so many interesting stories regarding peridot through the ages…

One of the earliest peridot mines to be exploited is the Egyptian Island of Zeberget in the Red Sea. My friend and mineralogical guru from years gone by, Dr. Peter Bancroft, did some “rock-hounding” for peridot on the island many years ago. At the time, he was allowed there as a co-traveler of Dr. Edward Gubelin the famous Swiss gemologist…

For those who don’t know, Dr. Gubelin was considered by many to be the father of European gemology (I was lucky enough as a young person to meet Dr. Gubelin and supply a few pieces for his world renowned personal collection).

Dr. Bancroft regaled me with several stories of their trip to Zeberget. Zeberget was considered to be of military importance to the Egyptian government at the time, so casual travel to the island was not allowed. Only the great credentials of Dr. Gubelin got them permission for the trip.

desert night camping

There being no commercial development on the island, the two men camped out on the desert landscape with only scorpions and cobras for company. Supposedly according to legend, one way to find the peridot there was to shine a light during the night-time and let exposed stones reflect back. Well they got a lot of eyes shining back at them instead. So they stopped that experiment!

Many of the peridot stones from Zeberget were easy to spot as such. They tended to have the actual crystal shape of olivine (peridot) but also to be sand-blasted by the desert sand over the millennia. The pitted surface of the stone is easily distinguished from stream-worn stones by use of 10X magnification. Both of these characteristics are rare. Most peridot of the world does not exhibit the crystal habit of olivine forming in massive formations or being found in formations where the gems have been broken by geological pressure through the years.

My dad was fortunate enough to acquire a truly fine Zeberget peridot many years ago in the late 1960’s. I eventually cut the gem and it was acquired for the gem collection of the Gemological Institute of America in the early 1980’s. Typical of all Zeberget peridot that I have seen this large gem was top color and exceptionally free from inclusions.

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The Color of Peridot

Peridot is uniquely interesting in its own way. While the color of emerald has laid claim to one of the most beautiful greens found in nature, peridot green has not found the same acceptance. Why this is, is not immediately evident. But there is a difference in the two colors.

High gem grade peridot is a beautiful grass green—balanced a little more towards the yellow as compared with emerald (as we have mentioned before in another blog post, green is a secondary color made up of the primary colors of blue and yellow).

Terminology: Olivine vs. Peridot

The official mineralogical name for Peridot is “olivine,” due to the fact that the largest quantities of this mineral are an olive green. The word “peridot” is reserved for gem quality material in a grass green color. Lower color qualities of this gem are an “olive green” and suitable only for matching with camouflage-green outfits.

There is some discussion about this in the gemological literature, much of it wildly erroneous. Olive green is generally considered to be brownish green. Brownish green is almost universally despised as a color for gems. Yet, due to the name “olivine” many people think that olive green is the “right” color for peridot. Not true. “Olivine” gets its name due to the fact that most olivine is olive green and that is what mineralogists were looking at when the mineral was officially described. Had this same logic occurred for diamonds there would be people out there singing the praises of straw colored diamonds—a truly downgraded color of diamond.

As we have stated, truly fine peridot is a nice grass green—not a color that has the brown look of olive green. Another descriptive word for high end peridot is “lime-green.” In any case beer-bottle green is the worst color for peridot. 🙂

Peridot meteor slab Esquel

Peridot The Space Gem

Another fun story about peridot is that it can truly be called the “space gem.” A once little known fact about peridot is that it can be found in meteorites. A relatively few meteorites have been found in the world bearing very pretty peridot crystals.

Officially, the astronomical community refers to this peridot under its scientific name of olivine. Olivine-bearing meteorites are referred to as Pallasites. The remaining portion of these meteorites is a metal composed primarily of nickel-iron.

From time to time I have seen these meteorites sawn into slabs and polished. They are quite lovely. When a light is shined from behind a cut and polished slab, the bright green of the peridot shines through and contrasts nicely against the darkness of the metal. When light is shined from the front the metal is quite bright and shiny and lovely and the peridot green still stands out. Age of these meteorites has been estimated in a way that puts them at the same age as planet Earth.

Peridot volcano

The Geology of Peridot

I was fortunate enough to sell some rough peridot and some custom faceted peridot to a research geologist at California Institute of Technology. As part of my visit I was able to discuss a little of the geology of peridot with the scientist.

Apparently peridot exists in great quantities at great depths in the earth. Molten peridot travels from the depths to the surface in the channels or tubes formed as volcanoes. Peridot has a very high melting point which means that peridot is one of the first things to solidify or crystallize as the magma of the volcano cools. Usually this happens in formations called basalt.

Lots of volcanic rock around the world occurs as basalt and there are probably deposits of peridot yet to be found. A guess I have would be Siberia, since there has been a lot of volcanic activity in parts of Siberia over the millennia—the diamond deposits of Siberia are evidence of that.

Diamonds are undeniably exciting but a new peridot mine would be fun as well!

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