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Peridot ( /ˈpɛr.ɪˌdɒt, -ˌdoʊ/ ''PERR-ih-dot, -⁠doh''), sometimes called chrysolite, is a deep yellowish-green transparent variety of
olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...
. Peridot is one of the few gemstones that only occurs in one color. Peridot can be found in
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...
and ultramafic rocks occurring in
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...
and peridotite
xenoliths A xenolith ("foreign rock") is a rock fragment (country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ign ...
of the
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
. The gem occurs in silica-deficient rocks such as volcanic
basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
and pallasitic meteorites. Peridot is one of only two gems observed to be formed not in the Earth’s crust, but in the molten rock of the upper mantle. Gem-quality peridot is rare on Earth's surface due to its susceptibility to weathering during its movement from deep within the mantle to the surface. Peridot has the formula of (Mg, Fe)2SiO4. Peridot is one of the birthstones for the month of August.


Etymology

The origin of the name ''peridot'' is uncertain. The ''
Oxford English Dictionary The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a c ...
'' suggests an alteration of AngloNorman (classical
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
-), a kind of
opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...
, rather than the
Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...
word , meaning "
gem A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, an ...
". The '' Middle English Dictionary''s entry on ''peridot'' includes several variations: , , and  — other variants substitute ''y'' for the ''i''s seen here. The earliest use in England is in the register of the St Albans Abbey, in Latin, and its translation in 1705 is possibly the first use of ''peridot'' in English. It records that on his death in 1245, Bishop John bequeathed various items, including peridot, to the Abbey.


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 Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
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 Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
concentrations.


Mineral properties


Crystal structure

The molecular structure of peridot consist 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 with 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 with rates increasing with temperature. The oxidation of the olivine occurs by initial breakdown of the fayalite component, and subsequent reaction with the forsterite component, to give
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With ...
and orthopyroxene.


Occurrence


Geologically

Olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...
, of which peridot is a type, is a common mineral in
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...
and
ultramafic rock Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are compose ...
s, often found in
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...
and in peridotite xenoliths of the
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
, 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. Olivine is an abundant mineral, but gem-quality peridot is rather rare due to its
chemical instability In chemistry, chemical stability is the thermodynamic stability of a chemical system. Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibriu ...
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 olivine is considered to be precious. In the ancient world, mining of peridot, called ''topazios'' then, on St. John's Island in the Red Sea began about 300 B.C. The principal source of peridot olivine today is the San Carlos Apache Indian Reservation in Arizona. It is also mined at another location in
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
, and in
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,
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
,
Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...
, and
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...
at Kilbourne Hole, in the US; and in
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
,
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,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
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,
Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...
,
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,
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(Burma),
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,
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,
Saudi Arabia Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in Western Asia. It covers the bulk of the Arabian Peninsula, and has a land area of about , making it the fifth-largest country in Asia, the second-largest in the Ara ...
,
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,
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
, and
Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...
.


In meteorites

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. Pallasitic (extraterrestrial) peridot differs chemically from its earthbound counterpart, in that pallasitic peridot lacks nickel.


Gemology

All minerals that are orthorhombic, like peridot, are biaxial and are defined by three principal axes: α, β, γ. Refractive index readings of faceted gems contain indices α = 1.653, β = 1.670, and γ = 1.689 with a corresponding biaxial birefringence of 0.036. The refractive index, as well as the specific gravity, slightly vary depending on the iron concentration; a dominant cause of peridot color variation. The numerical β index tends to shift towards the α and γ index with a corresponding increase in the iron concentration — forming the iron-rich end member fayalite. Study of Chinese peridot gem samples determined the specific gravity hydro-statically to be 3.36. The visible-light spectroscopy of the same Chinese peridot samples showed light bands between 493.0 and 481.0 nm, the strongest absorption at 492.0 nm. Inclusions are common in peridot crystals but their presence depend on the location it is found at and the geological conditions that led to the crystallization of the peridot. 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, seen often in San Carlos peridots, are a type of secondary negative crystal and are viewed easily under reflected light as circular discs surrounding a negative crystal. Silky and rod-like inclusions are common in Pakistani peridots. 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 Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can su ...
. These two types of mineral inclusions typically surrounded lily-pad cleavages. Biotite flakes appear flat, brown, translucent, and tabular. The largest cut peridot olivine is a specimen in the Smithsonian Museum in Washington, D.C.


Cultural history

Peridot has been prized since the earliest civilizations for its claimed protective powers to drive away fears and nightmares, according to superstitions. It is believed by some superstitious people to carry the gift of "inner radiance", sharpening the mind and opening it to new levels of awareness and growth, helping one to recognize and realize one’s destiny and spiritual purpose. There is no scientific evidence for such claims. Peridot is sometimes mistaken for emeralds and other green gems. Notable gemologist George Frederick Kunz discussed the confusion between emeralds and peridot in many
church Church may refer to: Religion * Church (building), a building for Christian religious activities * Church (congregation), a local congregation of a Christian denomination * Church service, a formalized period of Christian communal worship * Chri ...
treasure Treasure (from la, thesaurus from Greek language ''thēsauros'', "treasure store") is a concentration of wealth — often originating from ancient history — that is considered lost and/or forgotten until rediscovered. Some jurisdictions le ...
s, notably the " Three Magi" treasure in the Dom of
Cologne Cologne ( ; german: Köln ; ksh, Kölle ) is the largest city of the German western state of North Rhine-Westphalia (NRW) and the fourth-most populous city of Germany with 1.1 million inhabitants in the city proper and 3.6 millio ...
, Germany. Peridot olivine is the birthstone for the month of August.


Gallery

File:Peridot olivine on basalt.JPG, Peridot olivine with minor pyroxene, on vesicular
basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
. (field of view = 35 mm) File:Peridot-USGS.gif, Peridot from the San Carlos Apache Reservation in Arizona. File:Gemperidot.JPG, Olive green peridot File:Peridotgem.JPG, Peridot with milky inclusions


References


External links


Ganoksin


{{Portal bar, Minerals, Geology, Earth sciences Gemstones Silicate minerals