Peridot

Mike Sedlacek
March 10, 2010
ES 567: Gemstones of the World
Dr. Susan Aber, Instructor

Table of Contents:
  • Introduction
  • Chemical and Physical Properties
  • Occurrences of Peridot/Olivine
  • Uses of Peridot
  • Mystical Powers
  • References
  • Gemstones of the World Homepage

  • Figure 1: Olivine-faceted peridot-
    within a mafic rock. Picture taken
    from Aber (2010).


    Introduction

    Have you ever seen a transparent green gem? How about a transparent yellow gem? Chances are that if you have seen either gem, they might have been what gemologists call a peridot. Peridot gems can also be referred to as olivine, which is an iron and magnesium-rich mineral found on Earth. The word "peridot" is derived from the Arabic word "Zabargad", which means "peridot" (Mineral Miners, 2007). Peridot also has another variety, or type, called chrysolite, which is yellow colored. The word chrysolite is Greek for "yellow stone". A fair share of peridots are green though, which is how the mineral olivine got its name--from the color olive. Peridots have a unique history--ranging from how they formed and how the gems are used to the religious and spiritual beliefs related to peridot.

    Back To Top

    Chemical and Physical Properties

    The chemical composition of peridot is (Fe,Mg)2SiO4. Either iron or magnesium may be attached to the unit cell of peridot. This substitution of elements is what alters the color of peridot, ranging from olive green to yellow and brown. The color of peridot is also caused as a result of trace elements. Some trace elements include titanium and nickel (Mineral Miners, 2007). Peridot that is more green contains a higher percentage of the element magnesium. Peridot that is more yellow in color contains more iron.

    Some physical properties include:

  • Color: usually olive green or yellow; a less common color is brownish yellow (Schumann, 2000)
  • Streak: colorless
  • Hardness: 6.5-7 on the Mohs Hardness Scale
  • Density: 3.28-3.48 (depending on iron to magnesium content)
  • Cleavage: no cleavage; peridot tends to fracture instead in a conchoidal manner
  • Transparency: peridot is transparent
  • Luster: vitreous
  • Pleochroism: weak
  • Special Phenomenon: asterism or a star appearance and cat's eye chatoyancy; though both of these features are extremely rare (Schumann, 2000)

    Back To Top

    Occurrences of Peridot/Olivine

    Peridot is the gem form of olivine, which is a mineral found within oceanic rocks. Olivine is a mafic mineral, which means it is comprised of magnesium and iron. The word "mafic" is derived from those two elements--"ma" represents magnesium, and "fic" represents ferric, which is Latin for iron (Mineral Miners, 2007). Mafic minerals such as olivine are found in oceanic rocks such as basalt, gabbro, and dunite. These minerals make up the oceanic crust because they are denser than the minerals of continental crust; feldspar and silica minerals (Mineral Miners, 1997).

    Olivine, much like its cousins pyroxene and calcium, are mantle-derived minerals that are formed at very high temperatures directly above the mantle in oceanic crust (Keller, 1990). Peridot forms within this same environment, only as a solid within the oceanic crust. Most deposits of peridot occur as a result of a unique tectonic assemblage called an ophiolite (Keller, 1990). An ophiolite is a complete layer of oceanic crust that has overridden continental crust at a subduction zone. Ophiolites consist of distinct layers of mafic rocks ranging from dunite (pure olivine and peridot) at the bottom to basalt and sedimentary layers at the top. An example is shown in figure 2. Peridot can also form in a continental environment near subduction zones, though they are highly alkaline (Keller, 1990).

    Figure 2: A diagram from (West, 2006) shows an ophiolite sequence

    Peridot deposits are found in numerous parts of the world, including many locations with thick ophiolite sequences, such as Myanmar, Australia, Brazil, China, Kenya, Mexico, Pakistan, Tanzania, Arizona (USA), and Egypt. Of all of these, the most notable deposits are found in Pakistan and Egypt. One important ophiolite sequence that is found on Zabargad Island, Egypt, has historical significance that will be discussed later (Keller, 1990).

    Back To Top

    Uses of Peridot

    Peridot, as was just mentioned, can be found in a large ophiolite deposit on Zabargad Island, (also known as St. John Island) Egypt. This deposit has been important to the Egyptians for over three thousand years. Starting around 2000 B.C., Egyptians mined peridot for jewelry as well as for religious reasons. The mine on Zabargad Island was abandoned around 1500 and was later rediscovered around 1900 A.D. (Schumann, 2000).


    Figure 3: Faceted
    peridot. Picture from
    Gemstone.org
    Peridot became popular during the Crusades, when peridot was introduced to Europe for ecclesiastical purposes. Peridot became exceptionally popular during the Baroque period (~1500-1700 A.D.) in Europe. At that time, peridot became a favorite of wealthy monarchs. In the modern day, peridot is commonly used in the casting industry because of peridot's high melting point of 1200-1900 degrees Celsius, (Mineral Miners, 1997) and its hardness of 6.5-7 on the Mohs hardness scale. Peridot is commonly used today for jewelry and earrings (Mineral Miners, 2007). Most peridot gems are often cut in two different ways: Oval (faceted) and Octahedral (cabochon). Cabbing the stone is usually done when gems contain inclusions.

    Peridot gems tend to crack fairly easily, so peridot gems are cut very carefully. Peridot will not cleave when being cut, but they will fracture when too much stress is put on the gem. Another important thing to remember when purchasing or trying to identify a peridot is that there are gems that look like peridot such as chrysoberyl, diopside, emerald, and prehnite (Schumann, 2000). Mineral identification kits can be used to identify gem rough based on chemical and physical properties such as composition, cleavage-fracture, and transparency.

    Back To Top

    Mystical Powers

    A shroud of mystery has surrounded peridot for thousands of years. Different colors of peridot gems represent different things. For instance, an iron-rich, yellow peridot supposedly helps cure health problems associated with kidneys, the bladder, the gall bladder, and the stomach. A green, magnesium-rich peridot, on the other hand, represents financial success (Jewels).

    Peridot has been used to cure all sorts of health ailments for centuries. Jewels for me have suggested common ailments that peridot can "cure":

  • Peridot can heal ulcers, stop constipation, and cure bug bites by ingesting crushed Peridot. Move over ex-lax; an ancient cure has ousted you!
  • Peridot aids one's heart, thymus, lungs, and sleep by strengthening them with mystical powers.
  • Peridot can also be used to cure psychological problems.
  • Peridot can boost self-esteem, sooth nervousness, stop lethargy, and help one sleep better.
  • Would you like to reduce your stress? How would you like to destroy any resentment or jealousy you might have? If so, keep a peridot close!
  • Peridot is believed to counter the affects of negative emotions by acting as a detoxification agent if ingested.
  • If you have given birth, I hope you had a peridot gem with you. Peridot is believed to strengthen muscle contractions when placed on one's abdomen during childbirth.

  • Mineral Miners (2007) has some equally interesting ideas:
  • Move over Fountain of Youth - peridot is all you need to slow the aging process so long as you keep one at your side.
  • As if all of this isn't enough, if you are looking for a catch all, go no further. Peridot brings vitality to the whole body.
  • Peridot is associated with several astrological signs; Virgo, Leo, Libra, Scorpio, and Sagittarius, and is also the August birth gemstone.
  • Back To Top

    References

    For more information about peridot, visit this popular commercial peridot website: http://www.gemselect.com/other-info/history-peridot.php and this educational peridot website: http://realgems.org/list_of_gemstones/peridot.html.


    About This Webpage

    This website was created by Mike Sedlacek: March 13, 2010. It was created to fulfill an assignment for a graduate gemstone and gemology course from Emporia State University, http://www.emporia.edu. The ESU Earth Science Department homepage can be found at: http://www.emporia.edu/earthsci/earthsci.htm. I can be contacted at: msedlace@emporia.edu. Online May 10, 2010; last update May 12, 2010.

    Return to other student webpage examples at www.emporia.edu/earthsci/amber/go340/students/stupages.htm.

    Back To Top