Peridot: all you want to know about the green August birthstone.

May 06 2015 0 Comments

 

 

 

August is upon us, and the birthstone for this month is Peridot. To celebrate his olive green stone, I am going to be posting some information, curiosities & pics of jewellery designs I love made with this beautiful gem.

 

 

 

 

 

First of all, why the name Peridot?

 

According the Oxford English Dictionary, an alteration of Anglo-Norman “pedoretés” (Opal) is the origin of Peridot’s name. Another theory is that it is derived from the Arabic word "faridat” - the poor man’s emerald. Peridots were also called chrysolith (derived from the Greek word "goldstone") and olivine, because of its color.

 

 

Identifying a Peridot

 Peridot is a relatively easy stone to identify:

It is one of the few gemstones that occur only in olive green.

It is an iron magnesium silicate and the intensity of its green colour depends on how much iron is present in the crystal structure.

It has no resistance to acid.

It is known to form a cat's eye chatoyancy (asterism) in the form of four ray stars.

It’s strong double refraction is often a very distinguishing trait.

 

  

Peridot Gemology

 

Mineral: Olivine

Chemistry: (MgFe)2SiO4

Crystal System: orthorhombic

Density/Specific Gravity: 3.34

Mohs Hardness: 6.5 to 7.9

Refractive Index: 1.654-1.690

Birefringence: 0.035 to 0.038

 

Peridot Occurrence

 

Peridot is commonly founded in mafic rocks. It only occurs in a fraction of lavas and the mantle. Peridot forms in the magma, in the upper mantle, about 20 to 55 miles deep, and are brought to the surface by tectonic or volcanic activity. Peridot can be also found in meteorites. Recently, the “Hambleton meteorite” - a rare pallasite, stony-iron meteorite, resembling a fruitcake due to its peridot gemstones crystals - was auctioned in Edinburgh (photo). Read more about it here.
 The volcanic island Zabargad (St. John) in the Red Sea is a historically important deposit of Peridots.

                                                     

Peridot History and Lore  

Peridot is one of the oldest known gemstones in the world. Records document the mining of the gem as early as 1.500 B.C and it is believed that Cleopatra’s emerald collection could be actually Peridot.

Zabargard, a tiny island in Egypt, is documented as the first source of peridot, dating back as far as four thousand years. They used to call Peridots as “gem of the sun” which were supposed to protect against the terrors of the night. The island inhabitants were forced to extract the gems for the Pharaoh, working both night and day, as the gems could be found after nightfall due to their radiance.

The location of the island was lost for centuries and it was only rediscovered in  1905. In the 20th Century, the mines of Zabargad produced millions of dollars worth of peridot, but by the late 1930’s practically nothing was reached there anymore.

Peridot is mentioned in many ancient references as chrysolite. In those times, Peridot stones were used for carved talismans. It is mentioned throughout the Bible, and early Christians considered it sacred. Today, Catholic Bishops traditionally wear a ring of peridot and amethyst as a symbol of purity and morality.

In the Middle Ages, Europeans brought peridots back from the Crusades to decorate churches and robes. One of the most famous stone, adorning the shrine of the Three Holy Kings in the cathedral at Cologne was for centuries believed to be an emerald, but later rightly identified as Peridot.

The American Museum of Natural History in New York City and the Field Museum in Chicago, host two of the finest peridot specimens ever mined. The Smithsonian Institution in Washington DC has a cut peridot stone of 310 carats.





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