Peridot

General
Category| Silicate minerals
Formula
(repeating unit)| (Mg,Fe)
2SiO

Crystal system| Orthorhombic
Identification
Color| Yellow, to yellow-green, olive-green, to brownish, sometimes a lime green, to emerald hue
Twinning| Uncommon, simple twinning can occur on {100}, {011},{012}, cyclic twinning on {031}
Cleavage| Poor on {010} and {110}, {010} cleavage improves with increasing iron content
Fracture| Conchoidal
Mohs scale hardness| 6.5–7
|re|er}}| Vitreous to oily
Streak| Colorless
Diaphaneity| Translucent to transparent
Specific gravity| 3.2–4.3
Refractive index| 1.64–1.70
Birefringence| +0.036
Pleochroism| Weak pale yellow-green to yellow, yellow to yellow orange
Melting point| between 1,200 and 1,900°C
Fusibility| Infusible avoid thermal shock
Solubility| Slowly forms gelatinous silica in H Cl

Peridot (/ˈpɛrɪˌdɒt/ PERR-ih-dot), sometimes called chrysolite, is a yellow-green transparent variety of olivine. Peridot is one of the few gemstones that occur in only one color.

Peridot can be found in mafic and ultramafic rocks occurring in lava and peridotite xenoliths of the mantle. The gem occurs in silica-deficient rocks such as volcanic basalt and pallasitic meteorites. Along with diamonds, peridot is one of only two gems observed to be formed not in Earth's crust, but in the molten rock of the upper mantle.[1] Gem-quality peridot is rare on Earth's surface due to its susceptibility to alteration during its movement from deep within the mantle and weathering at the surface.[2] Peridot has a chemical formula of  (Mg,Fe)
2SiO

Peridot is one of the birthstones for the month of August.[3]

## Contents

* 1 Etymology
* 2 Appearance
* 3 Mineral properties
* 3.1 Crystal structure
* 3.2 Surface property
* 4 Occurrence
* 4.1 Geologically
* 4.2 In meteorites
* 5 Gemology
* 6 Cultural history
* 7 Gallery
* 8 Footnotes
* 9 References
* 10 External links

## Etymology

The origin of the name peridot is uncertain. The Oxford English Dictionary suggests an alteration of Anglo–Norman pedoretés (classical Latin pæderot-), a kind of opal, rather than the Arabic word faridat, meaning "gemstone".

The Middle English Dictionary's entry on peridot includes several variations: peridod, peritot, pelidod and pilidod — other variants substitute y for letter i used here.[4]

The earliest use of the word in English is possibly in the 1705 register of the St. Albans Abbey: The dual entry is in Latin with the translation to English listed as peridot. It records that on his death in 1245, Bishop John bequeathed various items, including peridot gems, to the Abbey.[5]

## Appearance

Peridot is one of the few gemstones that occur in only one color: an olive-green. The intensity and tint of the green, however, depends on the percentage of iron in the crystal structure, so the color of individual peridot gems can vary from yellow, to olive, to brownish-green. In rare cases, peridot may have a medium-dark toned, pure green with no secondary yellow hue or brown mask. Lighter-colored gems are due to lower iron concentrations.[6]

## Mineral properties

### Crystal structure

The atomic scale structure of olivine looking along the a axis. Oxygen is shown in red, silicon in pink, and magnesium/iron in blue. A projection of the unit cell is shown by the black rectangle.

The molecular structure of peridot consists of isomorphic olivine, silicate, magnesium and iron in an orthorhombic crystal system. In an alternative view, the atomic structure can be described as a hexagonal, close-packed array of oxygen ions with half of the octahedral sites occupied by magnesium or iron ions and one-eighth of the tetrahedral sites occupied by silicon ions.

### Surface property

Oxidation of peridot does not occur at natural surface temperature and pressure but begins to occur slowly at 600 °C (870 K) with rates increasing with temperature.[7] The oxidation of the olivine occurs by an initial breakdown of the fayalite component, and subsequent reaction with the forsterite component, to give magnetite and orthopyroxene.

## Occurrence

### Geologically

Olivine, of which peridot is a type, is a common mineral in mafic and ultramafic rocks, often found in lava and in peridotite xenoliths of the mantle, which lava carries to the surface; however, gem-quality peridot occurs in only a fraction of these settings. Peridots can also be found in meteorites.

Peridots can be differentiated by size and composition. A peridot formed as a result of volcanic activity tends to contain higher concentrations of lithium, nickel and zinc than those found in meteorites.[8][full citation needed]

Olivine is an abundant mineral, but gem-quality peridot is rather rare due to its chemical instability on Earth's surface. Olivine is usually found as small grains and tends to exist in a heavily weathered state, unsuitable for decorative use. Large crystals of forsterite, the variety most often used to cut peridot gems, are rare; as a result, peridot is considered to be precious.

In the ancient world, the mining of peridot was called topazios then, on St. John's Island, in the Red Sea began about 300 BCE.[9]

The principal source of peridot olivine today is the San Carlos Apache Indian Reservation in Arizona, US.[lower-alpha 1]

### In meteorites

Pallasite meteorite with olive-green peridot crystals, found in Fukang, China.

Peridot crystals have been collected from some pallasite meteorites. The most commonly studied pallasitic peridot belongs to the Indonesian Jeppara meteorite, but others exist such as the Brenham, Esquel, Fukang, and Imilac meteorites.[11] Pallasitic (extraterrestrial) peridot differs chemically from its earthbound counterpart, in that pallasitic peridot lacks nickel.[12]

## Gemology

Due to its high birefringence, doubling of facet junctions is commonly seen when viewing peridot under magnification.Due to its high birefringence, doubling of facet junctions is commonly seen when viewing peridot under magnification.

Orthorhombic minerals, like peridot, have biaxial birefringence defined by three principal axes: α, β, and γ. Refractive index readings of faceted gems can range around α = 1.651, β = 1.668, and γ = 1.689, with a biaxial positive birefringence of 0.037–0.038. With decreasing magnesium and increasing iron concentration, the specific gravity, color darkness and refractive indices increase, and the β index shifts toward the γ index. Increasing iron concentration ultimately forms the iron-rich end-member of the olivine solid solution series fayalite.[13]

A study of Chinese peridot gem samples determined the hydro-static specific gravity to be 3.36 . The visible-light spectroscopy of the same Chinese peridot samples showed light bands between 493.0–481.0 nm, the strongest absorption at 492.0 nm.[14]

The largest cut peridot olivine is a 310-carat (62-gram) specimen in the gem collection of the Smithsonian Museum in Washington, D.C.

Inclusions are common in peridot crystals but their presence depends on the location where it was found and the geological conditions that led to its crystallization.

* Primary negative crystals – rounded gas bubbles – form in situ with peridot, and are common in Hawaiian peridots.
* Secondary negative crystals form in peridot fractures.
* "Lily pad" cleavages are often seen in San Carlos peridots, and are a type of secondary negative crystal. They can easily be seen under reflected light as circular discs surrounding a negative crystal.
* Silky and rod-like inclusions are common in Pakistani peridots.[15]
* The most common mineral inclusion in peridot is the chromium-rich mineral chromite.
* Magnesium-rich minerals also can exist in the form of pyrope and magnesiochromite. These two types of mineral inclusions are typically surrounded "lily-pad" cleavages.
* Biotite flakes appear flat, brown, translucent, and tabular.[16]

## Cultural history

Peridot olivine is the birthstone for the month of August.[17]

Peridot has often been mistaken for emerald beryl and other green gems.[18] Noted gemologist G.F. Kunz discussed the confusion between beryl and peridot in many church treasures, most notably the "Three Magi treasure" in the Dom of Cologne, Germany.[19][1]

## Gallery

* Peridot olivine with minor pyroxene, on vesicular basalt. (field of view = 35 mm)

* Peridot from the San Carlos Apache Reservation in Arizona.

* Olive green peridot

* Peridot with milky inclusions

## Footnotes

1. ↑ "Although some good olive-colored crystals are found in a few other places, like Burma, China, Zambia, and Pakistan, ninety percent of all known peridots are found in just one place. It is a Native American reservation, and it is located in a little-visited corner of the United States: San Carlos." — V. Finlay[10]

## References

1. ↑ 1.0 1.1 "Peridot crystals: Formation & locations". Rock & Gem Magazine. 2023-07-10. https://www.rockngem.com/peridot-crystals/. Retrieved 2024-01-21. "Get to know this August birthstone".
2. ↑ "Peridot". The University of Texas. https://www.geo.utexas.edu/courses/347k/redesign/Gem_Notes/Peridot/peridot_main.htm.
3. ↑ "Color, meanings, and symbolism [of August birthstone peridot"]. Old Farmer's Almanac. https://almanac.com/august-birthstone-color-and-meaning.
4. ↑ Kuhn, Sherman M. (1982). "peridot". peridot. University of Michigan Press. p. 818 ff. ISBN 0-472-01163-4. https://books.google.com/books?id=XR52pY68WOUC&pg=PA818.
5. ↑ Ware, James, Sir (1705). The Antiquities and History of Ireland. A. Crook. p. 628 ff. https://books.google.com/books?id=gjrnAAAAMAAJ&pg=PA628.
6. ↑ Wise, Richard W. (2016). Secrets of the Gem Trade: The connoisseur's guide to precious gemstones (2nd ed.). Lenox, MA: Brunswick House Press. p. 220. ISBN 9780972822329.
7. ↑ Knafelc, Joseph; Filiberto, Justin; Ferré, Eric C.; Conder, James A.; Costello, Lacey; Crandall, Jake R. et al. (May 2019). "The effect of oxidation on the mineralogy and magnetic properties of olivine". American Mineralogist 104 (5): 694–702. doi:10.2138/am-2019-6829. ISSN 0003-004X. Bibcode: 2019AmMin.104..694K. https://pubs.geoscienceworld.org/ammin/article-abstract/104/5/694/570176/The-effect-of-oxidation-on-the-mineralogy-and.
8. ↑ Shen, A. (2011). "Identification of extraterrestrial peridot by trace elements". Gems & Gemology 47 (3): 208–213. doi:10.5741/GEMS.47.3.208.
9. ↑ "St. John's Island peridot information and history". http://www.mindat.org/loc-6423.html.
10. ↑ Finlay, Victoria (August 15, 2006). Jewels: A secret history (Kindle ed.). Ballantine Books. Kindle locations 543–546. ISBN 978-0345493354.
11. ↑ Leelawatanasuk, Thanong; Atichat, Wilawan; Thye Sun, Tay; Sriprasert, Boontawee; Jakkawanvibul, Jirapit (2014). "Some characteristics of taaffeite from Myanmar". The Journal of Gemmology 34 (2): 144–148. doi:10.15506/jog.2014.34.2.144. ISSN 1355-4565.
12. ↑ "Alien sightings: Pallasite". https://stonegrouplabs.com/wp-content/uploads/2021/06/0314GG-MarAprGMNPallasite.pdf.
13. ↑ Koivula, John I. (1981). "San Carlos peridot". Gems & Gemology 17 (4): 205–214. doi:10.5741/gems.17.4.205. https://www.gia.edu/doc/San-Carlos-Peridot.pdf. Retrieved 14 February 2023.
14. ↑ Koivula, John I.; Fryer, C.W. (1986-04-01). "The gemological characteristics of Chinese peridot". Gems & Gemology 22 (1): 38–40. doi:10.5741/GEMS.22.1.38. ISSN 0016-626X. http://www.gia.edu/gems-gemology/spring-1986-china-peridot-koivula.
15. ↑ "Sapat Gali, Naran, Kaghan Valley, Mansehra District, Khyber Pakhtunkhwa Province, Pakistan". https://www.mindat.org/loc-2536.html.
16. ↑ . Springer. 2009. pp. 87. doi:10.1007/978-3-540-72816-0_2288. ISBN 978-3-540-72795-8. https://link.springer.com/referenceworkentry/10.1007/978-3-540-72816-0_2288.
17. ↑ "Birthstones for each month". Gemological Institute of America. https://www.gia.edu/birthstones.
18. ↑ "Peridot gem guide and properties chart". https://www.gemstones.com/gemopedia/peridot.
19. ↑ Kunz, G.F. (June 1971). The Curious Lore of Precious Stones. New York, NY: Dover Publications. p. 66. ISBN 0-486-22227-6.

## External links

* Ganoksin
* Mineralminers
* USGS peridot data
* Emporia Edu
* Florida State University – Peridot

* v
* t
* e

Gemstones

Gemmological classifications by E. Ya. Kievlenko (1980), updated

Jewelry stones|

| 1st order|

* Diamond
* Ruby
* Emerald
* Blue Sapphire
* Alexandrite
* Natural marine pearls

|

2nd order|

* Pink sapphire
* Demantoid
* Tsavorite
* Spinel
* Precious Black Opal
* Tanzanite

3rd order|

* Yellow, Green, Violet Sapphires
* Aquamarine
* Orange topaz (Imperial)
* Rubellite
* Precious White and Fire Opal

4th order|

* Tourmaline — Verdelite
* Indicolite, polychromous
* Beryl]] — Heliodor, pink, yellow-green
* Topaz yellow, blue, pink
* Peridot
* Garnets — Spessartine (malaya), Rhodolite, Almandine, Pyrope
* Amethyst
* Citrine
* Blue Turquoise

Jewelry-Industrial
stones|

| 1st order|

* Lazurite
* Jadeite
* Nephrite
* Malachite
* Amber (Baltic amber)
* Chrysoprase
* Charoite

|

2nd order|

* Agate
* Amazonite
* Rhodonite
* Colorless, smoky and pink quartz
* Hematite
* Common opal
* Opaque iridescent feldspars

Industrial stones|

* Jasper
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* Cacholong (Porouse opal)
* Marble onyx
* Obsidian
* Listwanite (green mica)
* Jet
* Selenite
* Fluorite
* Serpentinite
* Aventurine quartzite
* Ophicalcite (Serpentine/Calcite)
* Pagodite (Pyrophyllite/Talc)

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Jewellery

Forms|

* Anklet
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Making|

| People|

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Processes|

* Carving
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Tools|

* Draw plate
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Materials|

| Precious metals|

* Gold
* Palladium
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* Rhodium
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|

Precious metal alloys|

* Britannia silver
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Base metals|

* Brass
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Mineral gemstones|

* Aventurine
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* Amazonite
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* Moonstone
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* Peridot
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* Sodalite
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* Sunstone
* Tanzanite
* Tiger's eye
* Topaz
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Organic gemstones|

* Abalone
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* Copal
* Coral
* Precious coral
* Black coral
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* Jet
* Nacre
* Operculum
* Pearl
* Tortoiseshell

Other natural objects|

* Bezoar
* Bog-wood
* Ebonite (vulcanite)
* Gutta-percha
* Hair
* Shell jewelry
* Spondylus shell
* Toadstone

Terms|

* Carat (mass)
* Carat (purity)
* Finding
* Millesimal fineness
* Art jewelry

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