Secondo una leggenda mostra la sua vera bellezza soltanto dopo il tramonto. A causa di questa convinzione è sempre stata associata alla mente subconscia ai sogni ed ai regni astrali.
Usata per migliorare il proprio intuito e le visioni, per i vaggi sciamanici e astrali, oppure come protezione dagli incubi se indossata nella notte oppure messa sotto il cuscino.
Si pensa che sia di ispirazione agli artisti e ai poeti, utile per il recupero del sé frammentato o per il recupero dell'anima.FONTE:
Peridot is a very pretty green stone that, according to legend, only shows its true beauty after nightfall. Because of this belief, Peridot has always been magically linked to the subconscious mind, dreams and the astral realms. Peridot is used in magic to improve your intuition and the confidence to trust your 'gut feelings' and intuitive insights. It is also used for dream magic, undertaking shamanic journeys and encouraging astral travel.
It is said that Peridot should be worn at night (or kept under your pillow) to protect against nightmares, night hags and vampires. Wearing Peridot is also said to help you keep your wits about you, especially in challenging situations, and protect you from foolishness, tactlessness and madness.
Peridot is believed to be a powerful crystal for emotional healing, able to help restore the missing or damaged fragments of a person's soul so that they can enjoy inner peace and contentment. Peridot is said to bring inspiration to poets and artists, along with the confidence and self-belief needed to realize your creative dreams. In other lore, Peridot is said to be able to guide you towards a happy marriage or true, loving friendships with like-minded people.
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Peridot2.jpgFONTE:
Da Wikipedia, l'enciclopedia libera.
La olivina, è un minerale silicatico che, insieme ai granati, fa parte dei neso-silicati, caratterizzati da tetraedri isolati di SiO4.
I tetraedri sono collegati attraverso atomi di magnesio o ferro con coordinazione . Il termine olivina comprende una serie isomorfa che va dalla forsterite (estremo magnesifero) alla fayalite (estremo ferrifero). Tali termini estremi sono praticamente inesistenti in natura.
Le olivine possono contenere calcio e manganese in sostituzione di ferro e magnesio. Il termine manganesifero è rappresentato dalla tefroite.
Campioni trasparenti di olivina vengono tagliati e lavorati con ottimi risultati.
L'abito cristallino è prismatico e tozzo, tale che qualunque sezione presenta un contorno più o meno esagonale.
Origine e giacitura
Le olivine sono costituenti fondamentali di molte rocce, soprattutto di quelle magmatiche ultramafiche e mafiche (povere di silice), sia intrusive che effusive, come le duniti (più del 90% di olivina), le peridotiti ed alcuni basalti. Le olivine rappresentano il primo minerale a cristallizzare da un fuso del mantello terrestre.
L'olivina può essere anche un prodotto del metamorfismo di contatto di medio e alto grado prevalentemente su rocce metamorfiche ultrabasiche (serpentinite) e, meno diffusamente, su rocce sedimentarie come dolomie, calcari dolomitici, rocce carbonatiche ricche in ferro. L'olivina metamorfica è rappresentata, di conseguenza, prevalentemente da termini puri particolarmente ricchi in Mg e Fe come forsterite (per reazione tra serpentino e diopside; per reazione anidra tra quarzo e dolomia o calcare dolomitico) e fayalite (per reazione tra quarzo e siderite). Per metamorfismo di contatto in condizioni idrate su dolomie, si origina, invece - per reazione con l'anfibolo - la tremolite. L'olivina è rinvenibile anche in vari gruppi di meteoriti condritiche e nel vulcano Vesuvio. E' instabile in presenza di quarzo, con il quale tende a reagire per formare l'enstatite, un silicato appartenente alla classe dei pirosseni. La reazione tra olivina e silice è:
Mg2SiO4 + SiO2 --> Mg2Si2O6 (Enstatite, ortopirosseno)
Forma in cui si presenta in natura
Si presenta in masse granulari di cristalli tozzi, dall'abito prismatico, con un colore variabile dal verde oliva al giallastro, bruno per alterazione.
Le olivine fondono a temperature molto elevate e vengono quindi usate come costituenti di materiali refrattari ed abrasivi, in apparecchi elettronici ad alta frequenza, per la costruzione di pellicole sottili, ceramiche, leghe e collanti per alte temperature. Esiste una varietà di olivina magnesiaca classificata come pietra semi-preziosa e nota come "peridoto", impiegata in gioielleria.
^ W.A. Deer, R. A. Howie, J. Zussman, Introduzione ai minerali che costituiscono le rocce, pp 11-12, Zanichelli Bologna 1994.
W.A. Deer, R. A. Howie, J. Zussman, Introduzione ai minerali che costituiscono le rocce, Zanichelli Bologna 1994 - ISBN 88-08-09882-6.
Walter Schumann. Guida alle gemme del mondo, Zanichelli.
John Sinkankas. Gemstone & Mineral Data Book, Winchester Press.
Attribuzione: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
FONTE IMMAGINE: http://commons.wikimedia.org/wiki/File:Forsterite-Olivine-tmu14a.jpg?uselang=itFONTE.
From Wikipedia, the free encyclopedia
Peridot (play /ˈpɛrɨdɒt/ or /ˈpɛrɨdoʊ/) is gem-quality forsteritic olivine.
The chemical composition of peridot is (Mg, Fe)2SiO4, with Mg in greater quantities than Fe.
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 "gem".
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 how much iron is contained in the crystal structure, so the color of individual peridot gems can vary from yellow- to olive- to brownish-green. The most valued color is a dark olive-green.
Peridot olivine is the birthstone for August.
Confusion with other gems
It is sometimes mistaken for emeralds and other green gems. In fact notable gemologist George Frederick Kunz discussed the confusion between emeralds and peridots in many church treasures, notably the "Three Magi" treasure in the Dom of Cologne, Germany.
Olivine, of which peridot is a type, is a common mineral in mafic and ultramafic rocks, and it is often found in lavas and in peridotite xenoliths of the mantle, which lavas carry to the surface; but gem quality peridot only occurs in a fraction of these settings. Peridot can be also found in meteorites.
Olivine in general is a very abundant mineral, but gem quality peridot is rather rare. This mineral is precious.
Locations of occurrence
Peridot olivine is mined in North Carolina, Arizona on the San Carlos Reservation, Hawaii, Nevada, and New Mexico, in the US; and in Australia, Brazil, China, Kenya, Mexico, Myanmar (Burma), Norway, Pakistan, Saudi Arabia, South Africa, Sri Lanka, and Tanzania.
Possibility of origin in Egypt
In much antique jewelry, peridot could have come from Egypt: in the late 18th century/early 19th century, peridot was taken from Egyptian ecclesiastial and other ornaments and reused in jewelry. Furthermore a location in Egypt was (re-) discovered but its location remains generally unknown.
Peridot crystals have been collected from some Pallasite meteorites. A famous Pallasite was offered for auction in April 2008 with a requested price of close to $3 million at Bonhams, but remained unsold.
The largest cut peridot olivine is a 310 carat (62 g) specimen in the Smithsonian Museum in Washington, D.C..
^ Kunz, Gems and Precious Stones, on Peridot
^ Church, Peridot Chapter
^ Fukang Meteorite auction at Bonhams
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Peridot_olivine_on_basalt.JPGFONTE:
From Wikipedia, the free encyclopedia
The mineral olivine (when gem-quality also called peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface.
The ratio of magnesium and iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember) and fayalite (Fe-endmember). Compositions of olivine are commonly expressed as molar percentages of forsterite (Fo) and fayalite (Fa) (e.g., Fo70Fa30). Forsterite has an unusually high melting temperature at atmospheric pressure, almost 1900 °C, but the melting temperature of fayalite is much lower (about 1200 °C). The melting temperature varies smoothly between the two endmembers, as do other properties. Olivine incorporates only minor amounts of elements other than oxygen, silicon, magnesium and iron. Manganese and nickel commonly are the additional elements present in highest concentrations.
Olivine gives its name to the group of minerals with a related structure (the olivine group) which includes tephroite (Mn2SiO4), monticellite (CaMgSiO4) and kirschsteinite (CaFeSiO4).
Identification and paragenesis
Olivine is named for its typically olive-green color (thought to be a result of traces of nickel), though it may alter to a reddish color from the oxidation of iron.
Translucent olivine is sometimes used as a gemstone called peridot, the French word for olivine. It is also called chrysolite, from the Greek words for gold and stone. Some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad island in the Red Sea.
Olivine/peridot occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica. That magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks such as peridotite and dunite can be residues left after extraction of magmas, and typically they are more enriched in olivine after extraction of partial melts. Olivine and high pressure structural variants constitute over 50% of the Earth's upper mantle, and olivine is one of the Earth's most common minerals by volume. The metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite.
Fe-rich olivine is relatively much less common, but it occurs in igneous rocks in small amounts in rare granites and rhyolites, and extremely Fe-rich olivine can exist stably with quartz and tridymite. In contrast, Mg-rich olivine does not occur stably with silica minerals, as it would react with them to form orthopyroxene ((Mg,Fe)2Si2O6).
Mg-rich olivine is stable to pressures equivalent to a depth of about 410 km within Earth. Because it is thought to be the most abundant mineral in Earth’s mantle at shallower depths, the properties of olivine have a dominant influence upon the rheology of that part of Earth and hence upon the solid flow that drives plate tectonics. Experiments have documented that olivine at high pressures (e.g., 12 GPa, the pressure at depths of about 360 kilometers) can contain at least as much as about 8900 parts per million (weight) of water, and that such water contents drastically reduce the resistance of olivine to solid flow; moreover, because olivine is so abundant, more water may be dissolved in olivine of the mantle than contained in Earth's oceans.
Mg-rich olivine has also been discovered in meteorites, on Mars and on the Moon. Such meteorites include chondrites, collections of debris from the early solar system, and pallasites, mixes of iron-nickel and olivine. The spectral signature of olivine has been seen in the dust disks around young stars. The tails of comets (which formed from the dust disk around the young Sun) often have the spectral signature of olivine, and the presence of olivine has recently been verified in samples of a comet from the Stardust spacecraft.
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Peridot_in_basalt.jpg
Olivine has also been identified in meteorites, the Moon, Mars, in the dust of comet Wild 2, within the core of comet Tempel 1, falling into infant stars, as well as on asteroid 25143 Itokawa.
Minerals in the olivine group crystallize in the orthorhombic system (space group Pbnm) with isolated silicate tetrahedra, meaning that olivine is a nesosilicate. 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.
There are three distinct oxygen sites (marked O1, O2 and O3 in figure 1), two distinct metal sites (M1 and M2) and only one distinct silicon site. O1, O2, M2 and Si all lie on mirror planes, while M1 exists on an inversion center. O3 lies in a general position.
High pressure polymorphs
At the high temperatures and pressures found at depth within the Earth the olivine structure is no longer stable. Below depths of about 410 km (250 mi) olivine undergoes a phase transition to the sorosilicate, wadsleyite and, at about 520 km (320 mi) depth, wadsleyite transforms into ringwoodite, which has the spinel structure. These phase transitions lead to a discontinuous increase in the density of the Earth's mantle that can be observed by seismic methods.
The pressure at which these phase transitions occur depends on temperature and iron content. At 800 °C (1,070 K; 1,470 °F), the pure magnesium end member, forsterite, transforms to wadsleyite at 11.8 gigapascals (116,000 atm) and to ringwoodite at pressures above 14 GPa (138,000 atm). Increasing the iron content decreases the pressure of the phase transition and narrows the wadsleyite stability field. At about 0.8 mole fraction fayalite, olivine transforms directly to ringwoodite over the pressure range 10.0–11.5 GPa (99,000–113,000 atm). Fayalite transforms to Fe2SiO4 spinel at pressures below 5 GPa (49,000 atm). Increasing the temperature increases the pressure of these phase transitions.
Olivine is one of the weaker common minerals on the surface according to the Goldich dissolution series. It weathers to iddingsite (a combination of clay minerals, iron oxides and ferrihydrites) readily in the presence of water. The presence of iddingsite on Mars would suggest that liquid water once existed there, and might enable scientists to determine when there was last liquid water on the planet.
A worldwide search is on for cheap processes to sequester CO2 by mineral reactions. Removal by reactions with olivine is an attractive option, because it is widely available and reacts easily with the (acid) CO2 from the atmosphere. When olivine is crushed, it weathers completely within a few years, depending on the grain size. All the CO2 that is produced by burning 1 liter of oil can be sequestered by less than 1 liter of olivine. The reaction is exothermic but slow. In order to recover the heat produced by the reaction to produce electricity, a large volume of olivine must be thermally well isolated. The end-products of the reaction are silicon dioxide, magnesium carbonate and small amounts of iron oxide.
The aluminium foundry industry uses olivine sand to cast objects in aluminium. Olivine sand requires less water than silicon based sand while providing the necessary strength to hold the mold together during handling and pouring of the metal. Less water means less gas (steam) to vent from the mold as metal is poured into the mold.
^ Klein, Cornelis; and C. S. Hurlburt (1985). Manual of Mineralogy (21st ed.). New York: John Wiley & Sons. ISBN 0-471-80580-7.
^ Smyth, J. R.; Frost, D. J.; Nestola, F.; Holl, C. M.; Bromiley, G. (2006). "Olivine hydration in the deep upper mantle: Effects of temperature and silica activity". Geophysical Research Letters 33 (15). doi:10.1029/2006GL026194.
^ Press Release 06-091. Jet Propulsion Laboratory Stardust website, retrieved May 30, 2006.
^ Fukang and other Pallasites
^ Pretty Green Mineral.... Planetary Science Research Discoveries, Hawaii Institute of Geophysics and Planetology
^ Mission Update 2006... UMD Deep Impact Website, University of Maryland Ball Aerospace & Technology Corp. retrieved June 1, 2010
^ Spitzer Sees Crystal Rain... NASA Website
^ Japan says Hayabusa brought back asteroid grains... retrieved November 18, 2010
^ Deer, W. A.; R. A. Howie, and J. Zussman (1992). An Introduction to the Rock-Forming Minerals (2nd ed.). London: Longman. ISBN 0-582-30094-0.
^ Kuebler; et al. (2003). "A Study of Olivine Alteration to Iddingsite Using Raman Spectroscopy". Lunar and Planetary Science 34: 1953.
^ Swindle, T. D.; et al. (2000). "Noble Gases in Iddingsite from the Lafayette meteorite: Evidence for Liquid water on Mars in the last few hundred million years". Meteoritics and Planetary Science 35 (1): 107–115. doi:10.1111/j.1945-5100.2000.tb01978.x.
^ Philip Goldberg et al. CO2 Mineral Sequestration Studies in US
^ Schuiling, R. D.; Krijgsman, P. (2006). "Enhanced Weathering: An Effective and Cheap Tool to Sequester Co2". Climatic Change 74: 349–354. doi:10.1007/s10584-005-3485-y.
^ The Guide to Rocks and Minerals
^ Ammen, C.W. (1980). The Metal Caster's Bible. Blue Ridge Summit PA: TAB. pp. 331. ISBN 0-8306-9970-8.
Attribution: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
FONTE IMMAGINE: http://commons.wikimedia.org/wiki/File:Ludwigite-Olivine-t06-333a.jpg