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Roger Weller, geology instructor

Rachel Fero

Physical Geology
Spring 2005

                       Olivine and Peridot                    .


Fig. 1. Rachel Fero. Olivine Pools. July 2004



          Last summer, my aunt and uncle brought me on a trip to Maui.  Before we went on the trip, my aunt gave me a book called Maui Revealed.  In that book, I read about the Olivine Pools.  On previous trips, my aunt and uncle had tried to find the Olivine Pools but they never found them, so, I did a little research on the internet and found exact directions with mile-post numbers and distances.  A couple days after we got to Maui, we went on a ride and found the Olivine Pools, right on time for my uncle’s birthday.  At the time I had wondered what olivine was.  I had never heard of it before and all the guide book said was “We called it the Olivine Pools because of its gem-like quality, the color of the area and the ample amounts of a semi-precious gem called olivine encrusted in the surrounding lava and sandstone” (Doughty 60).  I never did get around to looking it up.  Then, six months later, I ended up taking a geology class and found out that olivine is the same thing as peridot.

            Peridot, pronounced peridoe, is the gem variety of olivine, has the hardness of 6.5 to 7 and has poor cleavage in two directions at 90 degrees.  It breaks in conchoidal fractures.  Peridot is a magnesium-iron rich silicate mineral.  Its chemical formula is (MgFe)2SiO4.  The scientific name for peridot is Magnesium Iron Silicate.  There are two minerals in the same family that are similar to peridot, fayalite and forsterite.  Fayalite, Fe2SiO4, is rich in iron and forsterite, Mg2SiO4, is rich in magnesium.  Because of its iron content, fayalite is usually slightly darker and heavier than forsterite and peridot but they are hard to tell apart.  Since they are hard to tell apart, they are all usually called olivine.  “The best colored peridot has an iron percentage less than 15% and includes nickel and chromium as trace elements that may also contribute to the best peridot color” (Olivine).  The color of peridot ranges from light emerald green to pale yellowish green, which is the most common color.  Peridot can also be clear and greenish brown to black.  Olivine can be transparent or translucent and has a vitreous luster.

            Peridot forms as grains inside basalt.  After the basalt weathers, the peridot appears and can be easily found.  If you don’t want to wait for weathering, drilling and blasting is required.  The most common size of peridot that is found is about one carat but larger sizes can be found.  Flawless stones five carats and over are rare.

Peridot has been a favorite gemstone for jewelry for a long time.  Some people believe the emeralds Cleopatra wore were not emeralds, but peridot instead. 

“Peridot is the birthstone of August and is usually a very affordable colored gemstone.  Unfortunately it is often compared to the rich dark green of emerald and in this comparison it is often found lacking.  But peridot has its own unique green-yellow color that is different from emerald and this comparison is rather unfair” (Olivine).

Peridot is often worn because it is supposed to bring success, peace, and good luck.  It can be tumbled and set in baroque jewelry or even made into beads.  Peridot can also be used in mosaics but the most popular way to display peridot is faceted and set in rings, earrings, bracelets and in many other types of jewelry.  Olivine also has industrial uses such as refractory sands and abrasives.

            For years, the United States was the largest producer of peridot, but now there is competition from China and Pakistan.  The earliest known place peridot was produced was St. Johns Island in the Red Sea, which is about 54 kilometers away from the Egyptian coast.  Peridot was produced at St. Johns Island around 70 AD.  Burma, now called Myanmar, was famous for 20- to 40- carat stones which had great color and clarity.  Unfortunately, the socialist government took over and the supply of Burmese peridot disappeared.  “One can only guess as to whether the deposits are mined out, or if government policies have resulted in the shortage of material” (Gemstones). 

            In the United States, the most popular place for mining peridot is Arizona.  In fact, Peridot Mesa, Arizona is the world’s most productive location for peridot.  Peridot Mesa is located in Gila County on the San Carlos Apache Indian Reservation.  Approximately eighty to ninety percent of the production of the world’s peridot comes from that area.  Another location in Arizona is Buell Park Apache County.  There are also three locations in New Mexico where gem-quality peridot can be found.  In the northwestern quadrant of the state is the Buell Park area in McKinley County.  Near the Mexican border, there are two places which are Kilbourne Hole and Potrillo Mar depression.  The peridot in Kilbourne Hole is better than the peridot from the San Carlos Reservation in Arizona, but there is currently no commercial production of peridot in New Mexico.


Works Cited

            Amethyst Galleries Inc. Olivine (Magnesium Iron Silicate). 2002. 9 April 2005.
Doughty, Andrew, and Harriet Friedman. Maui Revealed: The Ultimate Guidebook. Lihu’e Hawai’i. Wizard Publications Inc., 2004.

            Fero, Rachel. Olivine Pools Picture. July 2004.

            United States Geological Survey. Gemstones-Peridot. 17 July 2002. 9 April 2005.