Welcome to Peter Indorf Designs Blog!

This issue is about Peridot and Spinel, the birthstones for August.  I hope you enjoy the materials here, which are courtesy of GIA.  

If you have any questions, comments or are interested in learning more about these gems or any other gems or jewelry, please get in touch at peter@peterindorf.com.  

The photo above show me working on a custom design for a client in my gem lab and library.

Thanks,

Peter

The ancient Egyptian’s called peridot the gem of the sun.

Peridot has has always been associated with light. Some believed that a protected it’s owner from “terrors of the night” especially when it was set in gold.  Others strung the gems to donkey hair and tied them around their left arm to ward off evil spirits.  The word peridot comes from the Arabic “faridat,” which means “gem.”  Most peridot formed deep inside the earth and was delivered to the service by volcanoes.  Some also came to the earth in meteorites, but this extraterrestrial peridot is extremely rare, and not likely to be seen in a retail jewelry store, although I have an example in my stock.  Peridot is the traditional birthstone for August.

Color

Peridot’s color ranges from yellowish green to greenish yellow. The most favored peridot color is a richly saturated pure grass green without any hint of yellow or brown, which is usually only achieved and gems of 10 carats or larger. Smaller examples tend to show yellowish green hues. Brown undertones lower the value of peridot.

Photo courtesy of Stuller, Inc.

The above gem examples are courtesy of Gem 2000 

Clarity

The best quality peridot has no eye-visible inclusions, with perhaps a few tiny black spots – minute mineral crystals – visible under magnification. Other inclusions common in peridot are reflective, dish shaped inclusions called “lily pads”.

Sources

Peridot is found as a regular nodules (rounded rocks with peridot crystals inside) in some lava flows in the United States and recently in Hawaii, China and Vietnam and, very rarely, as large crystals lining veins or pockets in certain types of solidified molten rock. Sources for the latter include Finland, Pakistan, Myanmar in the island of Zabargad.  The lighter material shown in the above photos are from Arizona and the richer colored gems are from Pakistan.

Moh’s Hardness

The hardness is 6.5 to 7 which is fine for daily wear.

Treatments

Peridot is rarely treated, but might have fractures that can be filled to improve the apparent clarity.

Care and cleaning

Clean only with warm soapy water. Ultrasonic and steam cleaners are never recommended.

A symbol of power, victory and new hope.

With increasing prominence, wide color range and reasonable prices, spinel is highly sought after by high-and jewelers.   This is a sleeper gem, if you love luscious color in a variety of hues, hardness, durability and beauty, take a closer look at spinel.  It’s a great value due to consumer confusion with synthetic spinel.  Natural spinel is rare and desirable.

The name spinel comes from the Latin “spina” meaning “thorn”, which refers to the shape of spinel crystals. Spinel has often been mistaken for other gemstones, especially ruby. The most famous 170 carat “Black Prince’s Ruby” given by the Spanish king to the Black Prince of England as payment for the battle victory, and the 361 carat “Timur Ruby” are actually fine large red spinels. The “Black Prince’s Ruby is now in the crown of the English Queen and resides in the Tower of London.  Fine specimens became the treasured property of kings and emperors.  In ancient times, the mines of central and southeast Asia yielded exceptionally large spinel crystals which became know as “Balas rubies.”  Some of these stones were the treasured property of kings an emperors, often passing through many hands as spoils of war.  As a result, some of the worlds most illustrious “rubies” are actually spinel.  Other large spinels are treasured in the royal collections of India, Russia and other countries.

Spinel crystals

Color

Spinel occurs in a range of hues, from orange to intense red, vibrant pink, and all shades of purple, blue and violet through blush green.  Intense reds and pinks are caused by traces of chromium.  Orange and purple stones contain a mixture of iron and chromium. Violet to blue spinel can be colored by iron, whereas rare vibrant blues owe their saturated color to cobalt.

The above gem examples are courtesy of Gem 2000

Clarity

Lighter colors of spinel are expected to be relatively free of inclusions but saturated reds and blues are rare and sometimes included.  The most valuable spinels have no eye-visible inclusions.  However, some spinels may have beautiful inclusions which reflect the gem’s octahedral crystal growth.  When they appear in groups, they resemble human fingerprints. 

Sources 

Fine large spinel crystal, historically referred to as “Balas rubies,” were mined in central and Southeast Asia.  Key mining locations are Myanmar, Tajikistan, Sri Lanka, Vietnam, and Tanzania. 

Mohs Hardness

With a hardness of 8, spinel is a great alternative to sapphire

Treatments
Some spinel might be subjected to heat treatment to improve clarity, but it is a stable treatment.  In rare cases, spinel may also be fracture-filled to improve its apparent clarity. 

Care and Cleaning

While ultrasonic cleaners and steam cleaners are usually safe, certain inclusions could pose a potential problem.  It’s always safe to clean spinel with warm, soapy water.

Information courtesy of Gemological Institute of America, GIA.edu