Carbonate Petrography

Carbonate petrography is the study of limestones, dolomites and associated deposits under optical or electron microscopes greatly enhances field studies or core observations and can provide a frame of reference for geochemical studies.

25 strangest Geologic Formations on Earth

The strangest formations on Earth.

What causes Earthquake?

Of these various reasons, faulting related to plate movements is by far the most significant. In other words, most earthquakes are due to slip on faults.

The Geologic Column

As stated earlier, no one locality on Earth provides a complete record of our planet’s history, because stratigraphic columns can contain unconformities. But by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column, that represents the entirety of Earth history.

Folds and Foliations

Geometry of Folds Imagine a carpet lying flat on the floor. Push on one end of the carpet, and it will wrinkle or contort into a series of wavelike curves. Stresses developed during mountain building can similarly warp or bend bedding and foliation (or other planar features) in rock. The result a curve in the shape of a rock layer is called a fold.

Showing posts with label gem stone. Show all posts
Showing posts with label gem stone. Show all posts

Pyrope

What is Pyrope?

Pyrope is the most well-known gemstone form of Garnet. The term Garnet describes a group name for several closely related minerals that form important gemstones, and Pyrope is an individual member mineral of the Garnet group. Its dark, blood-red colour is distinct and attractive, and makes a fine Garnet gemstone. In the gem trade, the term Pyrope is rarely used on its own. It is either generically called "Garnet", or "Pyrope Garnet".
The mineral pyrope is a member of the garnet group. Pyrope is the only member of the garnet family to always display red colouration in natural samples, and it is from this characteristic that it gets its name: from the Greek for fire and eye. The composition of pure pyrope is Mg3Al2(SiO4)3, although typically other elements are present in at least minor proportions-these other elements include Ca, Cr, Fe and Mn. Pyrope forms a solid solution series with almandine and spessartine, which are collectively known as the pyralspite garnets (pyrope, almandine, spessartine). Iron and manganese substitute for the magnesium in the pyrope structure. The resultant, mixed composition garnets are defined according to their pyrope-almandine ratio. The semi-precious stone rhodolite is a garnet of ~70% pyrope composition.
The origin of most pyrope is in ultramafic rocks, typically peridotite from the Earth's mantle: these mantle-derived peridotites can be attributed both to igneous and metamorphic processes. Pyrope also occurs in ultrahigh-pressure (UHP) metamorphic rocks, as in the Dora-Maira massif in the western Alps. In that massif, nearly pure pyrope occurs in crystals to almost 12 cm in diameter; some of that pyrope has inclusions of coesite, and some has inclusions of enstatite and sapphirine.
Pyrope is common in peridotite xenoliths from kimberlite pipes, some of which are diamond-bearing. Pyrope found in association with diamond commonly has a Cr2O3 content of 3-8%, which imparts a distinctive violet to deep purple colouration (often with a greenish tinge) and because of this is often used as a kimberlite indicator mineral in areas where erosive activity makes pin pointing the origin of the pipe difficult. These varieties are known as chrome-pyrope, or G9/G10 garnets.

History and Introduction

Pyrope garnet is the best known of the red garnets. It has a distinctive red colour that often resembles the colour of ruby or pomegranate seeds. The word "pyrope" comes from the Greek word "puropus", made up of "pur" (fire) and "ops" (eye) meaning "fiery-eyed". This refers to the impressive brilliance of pyrope garnet, which is a result of its high refractive index.
The use of red garnet dates back thousands of years, when it was used by Egyptian pharaohs for both decorative and ceremonial purposes. The ancient Romans also wore garnet rings and traded garnet gemstones. In ancient times, garnet and other red gemstones cut en cabochon were called "carbuncles", which is not the prettiest of names because it was also used to define pus-filled boils. Nowadays, any natural red gemstone cabochon can be traded as carbuncle stones.
The Latin word, "carbunculus" alludes to a burning piece of coal or ember. This may have been used to refer to garnet because of its bright colour large deposits of pyrope garnet were discovered in Bohemia (Central Europe) around the 16th century, which became the focus of the jewellery industry in the area. Bohemian pyrope garnet from the Czech Republic continues to be mined today.

Identifying Pyrope Garnet

Pyrope garnet is magnesium aluminium garnet. Iron can substitute for the magnesium and become more like almandine, which is iron aluminium garnet. Pure pyrope and pure almandine are rare in nature and most specimens are a mixture of the two. The change in density from almandine (4.3) to pyrope (3.6) is the only good test to determine a specimen's likely identity. Garnet can be distinguished from other gem types by its occurrence in metamorphic rock, its hardness (6.5 - 7.5 on the Mohs scale), colour, refractive index and cubic crystal structure. However, the quickest way to identify garnet is with the use of strong neodymium magnets. Garnet is attracted to neodymium magnets because it contains high concentrations of iron and/or manganese.

Origin and Gemstone Sources

Pyrope garnet sources include China, Madagascar, Myanmar, South Africa, Sri Lanka, Tanzania and the United States. Deposits in the Czech Republic do still exist, but are of minor importance.

Determining Pyrope Garnet Gemstone Value

Pyrope Garnet Colour

The characteristic dark-red of pyrope garnet is found in small sized stones. Bigger gems tend to be very dark, coming close to black.

Pyrope Garnet Clarity and Luster

Pyrope garnet is often inclusion free, so buyers should seek an "eye clean" stone. Pyrope garnet has a beautiful glossy vitreous luster.

Pyrope Garnet Cut and Shape

Pyrope garnet is versatile and can be cut into a wide variety of shapes. Pyrope garnet is not often seen in large sizes. It can be faceted or cut en cabochon. Faceted cuts best exhibit the beauty of pyrope garnet.

Pyrope Garnet Treatment

Pyrope garnet is not known to be treated or enhanced in any way.

Pyrope Metaphysical and healing properties

Pyrope Garnet offer us physical, emotional and spiritual support. Use its healing powers to boost circulation and blood disorders, as well as the digestive tract and immune system. Pyrope emotionally relieves anxiety, and promotes composure, courage and endurance. It lightens the overall mood. It protects the Base and Crown Chakras, and may balance the Heart and Brow Chakras as well.
Pyrope Garnet stimulates warmth and gentleness, unifying the creative forces of the self. On the spiritual path, it also helps open the heart to love - from Divine Love, as well as love of others.
Pyrope Garnets range in colour energies from rose red to deep crimson, including shades of scarlet, amethyst and indigo. It attracts a host of Angels and honours four Goddesses.
Garnet is the traditional birthstone of January, and Pyrope, in various hues, is a natural birthstone for many born at the end of summer through the winter. It is the zodiac stone for those born under the sign of Aquarius and it brings you Fire energy. As an Enhancer Strengthener crystal, it is a talisman of protection.

Properties of Pyrope

Chemical FormulaMg3Al2Si3O12
ColourRed
Hardness7 - 7.5
Crystal SystemIsometric
Refractive Index1.720 - 1.760
SG3.5 - 3.6
TransparencyTransparent to translucent
Double RefractionNone
LusterVitreous
CleavageNone
Mineral ClassPyrope (Garnet)

Pyrite (Marcasite)

What is Pyrite?

Pyrite, often called "Fools Gold", has a silvery-yellow to golden metallic colour. It is very common and may occur in large crystals. It has been used by ancient civilisations as jewellery, but is hardly used nowadays. Pyrite is sometimes incorrectly known as Marcasite in the gemstone trade. Marcasite is mineral that is a polymorph of Pyrite, and can be fragile and unstable, and is not fit for gemstone use.
The mineral pyrite, or iron pyrite, also known as fool's gold, is an iron sulphide with the chemical formula FeS2. This mineral's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold. The colour has also led to the nicknames brass, brazzle, and Brazil, primarily used to refer to pyrite found in coal.
Pyrite is the most common of the sulphide minerals. The name pyrite is derived from the Greek (pyritēs), "of fire" or "in fire", in turn from (pyr), "fire". In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what we now call pyrite. By Georgius Agricola's time, c. 1550, the term had become a generic term for all of the sulphide minerals.
Pyrite is usually found associated with other sulphides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds and as a replacement mineral in fossils. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold. Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37 wt% gold.

Occurrence of Marcasite

Marcasite can be formed as both a primary or a secondary mineral. It typically forms under low-temperature highly acidic conditions. It occurs in sedimentary rocks (shales, limestones and low grade coals) as well as in low temperature hydrothermal veins. Commonly associated minerals include pyrite, pyrrhotite, galena, sphalerite, fluorite, dolomite and calcite.
As a primary mineral it forms nodules, concretions and crystals in a variety of sedimentary rock, such as in the chalk layers found on both sides of the English Channel at Dover, Kent, England and at Cap Blanc Nez, Pas De Calais, France, where it forms as sharp individual crystals and crystal groups, and nodules.
As a secondary mineral it forms by chemical alteration of a primary mineral such as pyrrhotite or chalcopyrite.

Marcasite and Pyrite

A mineral is defined both by its chemical composition and its crystal structure. In some cases two different minerals have the same chemical composition, but different crystal structures. Known as polymorphs, these intriguing cases illustrate how the different crystal structures can result in quite different physical properties.
Perhaps the most famous case of a polymorph pair is diamond and graphite. Though both are composed entirely of pure carbon, diamond has a cubic structure with strong bonds in 3 dimensions. Graphite, by contrast, forms in layers with only weak bonds between layers. As a result of their structural differences, diamond has a hardness of 10 on the Mohs scale, while graphite rates only 1. Diamond is the ultimate abrasive, while graphite is a superb lubricant.
Another interesting polymorph pair is marcasite and pyrite. Both minerals are composed of iron sulphide. But where no one could ever confuse diamond and graphite, it can be difficult to tell pyrite and marcasite apart. In fact pyrite is often sold under the name marcasite in the gemstone trade. But despite their apparent similarities, they have some important differences, such that one can be used as a gem material while the other cannot.
Pyrite has a cubic structure, metallic luster and a yellow-gold colour that has earned it the nickname "fool's gold". With a hardness of 6 to 6.5 on the Mohs scale, pyrite is hard enough to be used in jewellery. Pyrite is also exceptionally dense, with a specific gravity of 5.0 to 5.2. Only hematite has a higher density.
Marcasite tends to be lighter in colour, and is sometimes referred to as "white iron pyrite". Sometime marcasite has a greenish tint, or a multi-coloured tarnish that is the result of oxidation. But marcasite has an unstable orthorhombic crystal structure and is liable to crumble and break apart. In some cases marcasite will react with moisture in the air to produce sulphuric acid. For these reasons marcasite is never used in jewellery. When a gemstone is sold as marcasite you can be quite sure that it is actually pyrite.

Varieties and blends

Blueite (S.H.Emmons): Nickel variety of marcasite, found in Denison Drury and Townships, Sudbury Dist., Ontario, Canada.
Lonchidite (August Breithaupt): Arsenic variety of marcasite, found at Churprinz Friedrich August Erbstolln Mine (Kurprinz Mine), Großschirma Freiberg, Erzgebirge, Saxony, Germany; ideal formula Fe(S, As)2.
Synonyms for this variety:
  • kausimkies,
  • kyrosite,
  • lonchandite,
  • metalonchidite (Sandberger) described at Bernhard Mine near Hausach (Baden), Germany.
Sperkise designates a marcasite having twin spearhead crystal. Sperkise derives from the German Speerkies (Speer meaning spear and Kies gravel or stone). This twin is very common in the marcasite of a chalky origin, particularly those from the Cap Blanc Nez.

Properties of Pyrite (Marcasite)

ColourMetallic, Yellow, Gray
Hardness6 - 6.5
Crystal SystemIsometric
SG4.9 - 5.2
TransparencyOpaque
Double RefractionNone
LusterMetallic
CleavageNone
Mineral ClassPyrite

Prehnite

What is Prehnite?

Prehnite is an inosilicate of calcium and aluminium. Prehnite crystallises in the orthorhombic crystal system, and most often forms as stalactitic or botryoidal aggregates, with only just the crests of small crystals showing any faces, which are almost always curved or composite. Very rarely will it form distinct, well-individualised crystals showing a square-like cross-section, including those found at the Jeffrey Mine in Asbestos, Quebec, Canada. Prehnite is brittle with an uneven fracture and a vitreous to pearly luster. Its hardness is 6-6.5, its specific gravity is 2.80-2.90 and its colour varies from light green to yellow, but also colourless, blue, pink or white. In April 2000, rare orange prehnite was discovered in the Kalahari Manganese Fields, South Africa. Prehnite is mostly translucent, and rarely transparent.
Though not a zeolite, prehnite is found associated with minerals such as datolite, calcite, apophyllite, stilbite, laumontite, heulandite etc. in veins and cavities of basaltic rocks, sometimes in granites, syenites, or gneisses. It is an indicator mineral of the prehnite-pumpellyite metamorphic facies.

History and Introduction

Prehnite is a translucent to transparent gem-quality hydrated calcium aluminum silicate. It was the first mineral to be named after an individual, and it was also the first mineral to be described from South Africa, long before South Africa became one of the most important sources for precious and semi-precious gems. It was first described in 1788 after it was discovered in the Karoo dolerites of Cradock, South Africa. Prehnite was later named after its discoverer, Colonel Hendrik von Prehn (1733-1785), a Dutch mineralogist and an early governor of the Cape of Good Hope colony.
Until recently, prehnite was a rare collector's gemstone, but new deposits have now made it more readily available. In China, prehnite is sometimes referred to as 'grape jade' owing to its typical nodule formations which often resemble a bunch of grapes. Its colour is usually a soft apple-green, which is quite unique to prehnite, but it can also occur in rarer colours including yellow, orange and blue.

Identifying Prehnite

Prehnite is typically semi-transparent to translucent with a chemical formula of Ca2Al(AlSi3O10)(OH)2. Its color is usually yellow-green to apple-green. Prehnite is considerably hard with a rating of 6 to 6.5 on the Mohs scale. It has a specific gravity ranging from 2.82 to 2.94 and a refractive index of 1.611 to 1.669. Prehnite is in the orthorhombic crystal class, usually found in radiating botryoidal (grape-like) aggregate forms, and rarely as tabular and pyramidal crystals. When heated, prehnite crystals can sometimes give off water. It has a brittle tenacity and an uneven fracture. When polished, prehnite has a vitreous to pearly luster. Prehnite may be confused with apatite, jade or serpentine.

Prehnite: Origin and Sources

Prehnite occurs in the veins and cavities of mafic volcanic rock. It is a typical product of low-grade metamorphism. Primary deposits of prehnite are sourced from several locations around the world. Some of the most important deposits come from Africa (Namibia, South Africa), Australia (Western Australia, Northern Territory), Canada, China, Germany, Scotland, France and the United States (New Jersey, Pennsylvania and Virginia).
Rare, orange coloured prehnite has been discovered in South Africa. Quebec, Canada is known to produce prehnite with distinct, individual crystals.

Prehnite: Related or Similar Gemstones

There are no closely related gemstones, but there are several gemstones which can have a very similar appearance (colour and luster), including jade, apatite, serpentine, brazilianite, periclase, chrysoprase, peridot, smithsonite and hemimorphite. Prehnite is also often found and associated with many microporous, aluminosilicate zeolite minerals such as datolite, calcite, apophyllite, stilbite and heulandite.

Prehnite Healing properties

Prehnite is considered a stone of unconditional love and the crystal to heal the healer. It enhances precognition and inner knowing. Enables you always to be prepared. Prehnite calms the environment and brings peace and protection. It teaches how to be in harmony with nature and the elemental forces. Helpful for “decluttering” letting go of possessions you no longer need, aiding those who hoard possessions, or love, because of an inner lack. Prehnite alleviates nightmares, phobias and deep fears, uncovering and healing the dis-ease that creates them. It is a stone for dreaming and remembering. Beneficial for hyperactive children and the causes that underlie the condition.
Prehnite heals the kidneys and bladder, thymus gland, shoulders, chest and lungs. It treats gout and blood disorders. Prehnite repairs the connective tissue in the body and can stabilise malignancy.

Properties of Prehnite

Chemical FormulaCa2Al2Si3O12(OH)
ColourGreen
Hardness6 - 6.5
Crystal SystemOrthorhombic
Refractive Index1.61 - 1.64
SG2.8 - 3.0
TransparencyTranslucent
Double Refraction.030
LusterVitreous, waxy
Cleavage1,1;3,1
Mineral ClassPrehnite

Platinum

What is Platinum?

Platinum is the most valued precious metal; its value exceeds even that of Gold. It has a beautiful silver-white colour, and, unlike Silver, does not tarnish. It is unaffected by common household chemicals and will not get damaged or discoloured by chlorine, bleach, or detergents. It is tougher than all precious jewellery metals, though due to its flexible tenacity it still must be alloyed with other metals to prevent it from bending. Natural Platinum usually contains small amounts of the rare element iridium. In jewellery, iridium is alloyed with the Platinum to increase its toughness. Platinum jewellery is usually 90 to 95 percent pure.
Platinum is one of the least reactive metals. It has remarkable resistance to corrosion, even at high temperatures, and is therefore considered a noble metal. Consequently, platinum is often found chemically uncombined as native platinum. Because it occurs naturally in the alluvial sands of various rivers, it was first used by pre-Columbian South American natives to produce artefacts. It was referenced in European writings as early as 16th century, but it was not until Antonio de Ulloa published a report on a new metal of Colombian origin in 1748 that it began to be investigated by scientists.
Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewellery. Being a heavy metal, it leads to health issues upon exposure to its salts; but due to its corrosion resistance, metallic platinum has not been linked to adverse health effects. Compounds containing platinum, such as cisplatin, oxaliplatin and carboplatin, are applied in chemotherapy against certain types of cancer.

About Platinum

  • Atomic number (number of protons in the nucleus): 78
  • Atomic symbol (on the periodic table of elements): Pt
  • Atomic weight (average mass of the atom): 195.1
  • Density: 12.4 ounces per cubic inch (21.45 grams per cubic cm)
  • Phase at room temperature: solid
  • Melting point: 3,215.1 degrees Fahrenheit (1,768.4 degrees Celsius)
  • Boiling point: 6,917 F (3,825 C)
  • Number of natural isotopes (atoms of the same element with a different number of neutrons): 6. There are also 37 artificial isotopes created in a lab.
  • Most common isotopes: Pt-195 (33.83 percent of natural abundance), Pt-194 (32.97 percent of natural abundance), Pt-196 (25.24 percent of natural abundance), Pt-198 (7.16 percent of natural abundance), Pt-192 (0.78 percent of natural abundance), Pt-190 (0.01 percent of natural abundance)

Platinum History (The "unmeltable" metal)

In ancient times, people in Egypt and the Americas used platinum for jewellery and decorative pieces, often times mixed with gold. The first recorded reference to platinum was in 1557 when Julius Scaliger, an Italian physician, described a metal found in Central America that wouldn't melt and called it "platina," meaning "little silver." 
In 1741, British scientist Charles Wood published a study introducing platinum as a new metal and described some of its attributes and possible commercial applications, according to Peter van der Krogt a Dutch historian. Then, in 1748, Spanish scientist and naval officer Antonio de Ulloa published a description of a metal that was unworkable and unmeltable. (He originally wrote it in 1735, but his papers were confiscated by the British navy.) 
Back in the 18th century, platinum was the eighth known metal and was known as "white gold," according to van der Krogt. (Previously known metals included iron, copper, silver, tin, gold, mercury and lead.)
In the early 1800s, friends and colleagues William Hyde Wollaston and Smithson Tennant, both British chemists, produced and sold purified platinum that they isolated using a technique developed by Wollaston, according to van der Krogt This technique involves dissolving platinum ore in a mixture of nitric and hydrochloric acids (known as aqua regia). After the platinum was separated from the rest of the solution, palladium, rhodium, osmium, iridium, and later ruthenium were all discovered in the waste.
Today, platinum is still extracted using a technique similar to that developed by Wollaston. Samples containing platinum are dissolved in aqua regia, are separated from the rest of the solution and byproducts, and are melted at very high temperatures to produce the metal.

Occurrence of Platinum

Platinum is an extremely rare metal, occurring at a concentration of only 0.005 ppm in Earth's crust. It is sometimes mistaken for silver (Ag). Platinum is often found chemically uncombined as native platinum and as alloy with the other platinum-group metals and iron mostly. Most often the native platinum is found in secondary deposits in alluvial deposits. The alluvial deposits used by pre-Columbian people in the Chocó Department, Colombia are still a source for platinum-group metals. Another large alluvial deposit is in the Ural Mountains, Russia, and it is still mined.
In nickel and copper deposits, platinum-group metals occur as sulfides (e.g. (Pt,Pd)S), tellurides (e.g. PtBiTe), antimonides (PdSb), and arsenides (e.g. PtAs2), and as end alloys with nickel or copper. Platinum arsenide, sperrylite (PtAs2), is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. At Platinum, Alaska, about 17,000 kg (550,000 ozt) had been mined between 1927 and 1975. The mine ceased operations in 1990. The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Gauteng, South Africa.
In 1865, chromites were identified in the Bushveld region of South Africa, followed by the discovery of platinum in 1906. The largest known primary reserves are in the Bushveld complex in South Africa. The large copper–nickel deposits near Norilsk in Russia, and the Sudbury Basin, Canada, are the two other large deposits. In the Sudbury Basin, the huge quantities of nickel ore processed make up for the fact platinum is present as only 0.5 ppm in the ore. Smaller reserves can be found in the United States, for example in the Absaroka Range in Montana. In 2010, South Africa was the top producer of platinum, with an almost 77% share, followed by Russia at 13%; world production in 2010 was 192,000 kg (423,000 lb).
Platinum deposits are present in the state of Tamil Nadu, India.
Platinum exists in higher abundances on the Moon and in meteorites. Correspondingly, platinum is found in slightly higher abundances at sites of bolide impact on Earth that are associated with resulting post-impact volcanism, and can be mined economically; the Sudbury Basin is one such example.

Properties of Platinum

Chemical FormulaPt
ColourMetallic, White
Hardness4 - 4.5
Crystal SystemIsometric
SG14 - 19
TransparencyOpaque
Double RefractionNone
LusterMetallic
CleavageNone
Mineral ClassPlatinum

Peridot

What is Peridot?

Peridot is a well-known and ancient gemstone, with jewellery pieces dating all the way back to the Pharaohs in Egypt. The gem variety of the mineral Olivine, it makes a lovely light green to olive-green gemstone. The intensity of colour depends on the amount of iron present in a Peridot's chemical structure; the more iron it contains the deeper green it will be. The most desirable colour of Peridot is deep olive-green with a slight yellowish tint. Deeper olive-green tones tend to be more valuable than lighter coloured greens and yellowish-greens.
Peridot is the gem variety of the mineral olivine. Its chemical composition includes iron and magnesium, and iron is the cause of its attractive yellowish green colours. The gem often occurs in volcanic rocks called basalts, which are rich in these two elements.
The glorious yellow-green Peridot has been under-appreciated for years, overlooked as a lesser gem, small, easily obtained and relatively inexpensive, often considered as simply the birthstone for August. Its popularity has fallen in and out of vogue for centuries. However, a new resurgence is bringing to light what Peridot lovers have always known: this is a truly remarkable stone.
Called “the extreme gem” by the Gemological Institute of America, Peridot is born of fire and brought to light, one of only two gems (Diamond is the other) formed not in the Earth’s crust, but in molten rock of the upper mantle and brought to the surface by the tremendous forces of earthquakes and volcanoes. While these Peridots are born of Earth, other crystals of Peridot have extraterrestrial origins, found in rare pallasite meteorites (only 61 known to date) formed some 4.5 billion years ago, remnants of our solar system’s birth. Peridot in its basic form, Olivine, was also found in comet dust brought back from the Stardust robotic space probe in 2006, has been discovered on the moon, and detected by instrument on Mars by NASA’s Global Surveyor. Ancients believed, quite accurately, that Peridot was ejected to Earth by a sun’s explosion and carries its healing power.

History and Introduction

Peridot is a gem-quality variety of the mineral olivine. It belongs to the forsterite-fayalite mineral series. Some even refer to peridot as 'olivine', but when it comes to the gemstone, 'peridot' is the correct term. Peridot is an idiochromatic gem, meaning its colour comes from the basic chemical composition of the mineral itself and not from minor traces of impurities. Thus, peridot is found only in green. In fact, peridot is one of the few gemstones available that can be found only in one color, although the shades of green may vary from light yellowish to dark brownish-green.
The name 'peridot' was derived from the Arabic word for gem 'faridat'. It is sometimes referred to as 'the poor man's emerald' or as 'chrysolite', a word derived from the Greek word 'goldstone'. It is one of the oldest known gemstones, with records dating back as early as 1500 B.C. Historically, the volcanic island of Zabargad (St. John) in the Red Sea, east of Egypt, had the most important deposit that was exploited for over 3500 years. Today, the finest quality peridot comes from Mogok in Burma, although Pakistani peridot is now highly regarded as well. There are other very important deposits found in Arizona, China and Vietnam. Peridot has also been discovered in fallen meteors and it has also been discovered on Mars and the moon in olivine form.

Occurrence of Peridot

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. Peridots can be also found in meteorites.
Olivine in general is a very abundant mineral, but gem quality peridot is rather rare. This is due to the mineral's chemical instability on the 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 meteorites

Peridot crystals have been collected from some pallasite meteorites.

Identifying Peridot

Chemically, peridot is an iron magnesium silicate and its intensity of colour depends on the amount of iron it contains. There may also be traces of nickel and chromium present. Peridot is not especially hard and it has no resistance to acid. On very rare occasions, peridot is known to form with cat's eye chatoyancy (asterism) in the form of four ray stars. Peridot can be mistaken for similar coloured gems, but its strong double refraction is often a very distinguishing trait. In thicker stones, the doubling of lower facet edges can be easily seen by looking down though the table without the need for magnification.

Peridot: Origin and Sources

Most gemstones are formed in earth's crust, but peridot is formed much deeper in the mantle region. Peridot crystals form in magma from the upper mantle and are brought to the surface by tectonic or volcanic activity where they are found in extrusive igneous rocks. Historically the volcanic island Zabargad (St. John) in the Red Sea was the location of the most important deposit. It was exploited for 3500 years before it was abandoned for many centuries; later, it was rediscovered around 1900 and has been heavily exploited ever since.
Today, the most important deposits are found in Pakistan (in the Kashmir region and the Pakistan-Afghanistan border region). Beautiful material is also found in upper Myanmar (Burma) and Vietnam. Other deposits are found in Australia (Queensland), Brazil (Minas Gerais), China, Kenya, Mexico, Norway (north of Bergen), South Africa, Sri Lanka, Tanzania and the United States (Arizona and Hawaii). Recently, China has become of the the largest producers of peridot.

Peridot: Related or Similar Gemstones

Peridot is a transparent gem variety of olivine. Olivine is not officially a mineral but is composed of two end-member minerals: fayalite and forsterite. Fayalite is iron rich olivine, while forsterite is magnesium rich olivine. Although iron is the colouring agent for peridot, it is technically closer to forsterite than fayalite with regard to chemical composition.
Peridot is sometimes referred to as 'chrysolite', a historical name which archaically refers to several green to yellow-green coloured gemstones. Other forms of 'chrysolite' include chrysoberyl, zircon, tourmaline, topaz and apatite.

Peridot Metaphysical and Healing properties

Peridot is highly beneficial for attuning to and regulating the cycles of one’s life, such as physical cycles, mental or emotional phases, as well as intellectual progression. It also helps dissipate negative patterns and old vibrations that play over and over, keeping one from realising they are deserving of success. By working with Peridot one can remove those blockages and move forward quickly, opening the heart and mind more fully to receive from the Universe with grace and gratitude.
A stone of transformation, Peridot is excellent for use in recovery from tobacco or inhalant dependencies, as well as other addictions. More importantly, it is a wounded healer stone, serving as a vital guide in facilitating healing processes that help others going through what you have already overcome. It is considered very effective in amplifying Reiki energies. Hold immediately after treatments using heat or warmth, such as sweat lodges, hot rocks or a sauna to continue the beneficial effects. 
Peridot is ideal for discharging emotional issues that affect the physical body. Place it over the Solar Plexus to relax and release nervous tension, known as “butterflies,” as well as to alleviate fear and guilt, anxiety or impatience. Place Peridot over the Heart Chakra to relieve heaviness of heart, empower forgiveness, or alleviate destructive jealousy or self-doubt caused by betrayal in past relationships. 
Use Peridot to gain results when seeking items that are lost or mislaid in the physical world, as well as in the quest for an enlightened state. 
Wear Peridot set in gold to bring peaceful sleep. It is especially effective for those who suffer from recurring nightmares about evil spirits, murders or sexual attacks. 
Wear or carry Peridot as a talisman of luck and as a sun stone to prevent personal darkness. It adds charm and eloquence to your presentations, evokes a positive, helpful response from normally unhelpful people, and increases profit in trades. It is naturally protective against envy, gossip behind your back, and people who would deceive you.

Properties of Peridot

Chemical Formula(Mg,Fe)2SiO4
ColourGreen, Yellow
Hardness6.5 - 7
Crystal SystemOrthorhombic
Refractive Index2.63 - 2.65
SG1.54 - 1.55
TransparencyTransparent
Double Refraction.009
LusterVitreous
Cleavage2,1 ; 3,1
Mineral ClassOlivine

Pearl gemstone

What is Pearl Gemstone?

A pearl is a hard object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of a clam, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes (baroque pearls) occur. The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries. Because of this, pearl has become a metaphor for something rare, fine, admirable and valuable.
The most valuable pearls occur spontaneously in the wild, but are extremely rare. These wild pearls are referred to as natural pearls. Cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those currently sold. Imitation pearls are also widely sold in inexpensive jewellery, but the quality of their iridescence is usually very poor and is easily distinguished from that of genuine pearls. Pearls have been harvested and cultivated primarily for use in jewellery, but in the past were also used to adorn clothing. They have also been crushed and used in cosmetics, medicines and paint formulations.
Whether wild or cultured, gem-quality pearls are almost always nacreous and iridescent, like the interior of the shell that produces them. However, almost all species of shelled mollusks are capable of producing pearls (technically "calcareous concretions") of lesser shine or less spherical shape.

History and Introduction

Pearls are organic gemstones that are formed by shelled molluscs; mainly bivalved oysters and mussels. Pearls are made up of nacre (mother-of-pearl) which is mostly aragonite (calcium carbonate) and conchiolin (complex proteins that form mollusc shells). The aragonite microcrystals build up around an irritant. The name "pearl" is said to have originated from the Middle English word "perle", which in turn came from the Latin word "perna", meaning "leg", thought to be due to the ham-leg shape of the bivalve mollusc.
Natural pearls are extremely rare, incredibly expensive and typically small. Therefore people have developed ways to culture pearls, so that these beautiful gemstones can be enjoyed by many. In cultured pearls, some tissue or a mother-of-pearl bead is introduced into the mollusc shell. If successful, this process induces the animal to form a "pearl sac" whose cells secrete a layer of brownish protein called conchiolin over the irritant. This is followed by the secretion of numerous mineral layers of nacre composed of calcium carbonate in thin overlapping plates. Pearls can come from fresh or seawater molluscs. The beauty of pearls is that they can be plucked from the shell naturally beautiful, fully-formed and displaying perfect lustre with no need to be cut or polished.
The oldest recorded reference to pearls in history is the 7,500 year-old "Umm Al Quwain Pearl", which was found in a grave in a place that is now known as the UAE. Before pearls were cultured by man, they were harvested from the Persian Gulf, Sri Lankan waters, fresh water sources in China and the rivers of Europe. Later, Christopher Columbus discovered pearls in South America. When these natural pearls were almost depleted in the early twentieth century, the Chinese and Japanese began to culture pearls and the rest is history. Nowadays, pearls remain a treasured adornment and are cultured all around the world.

Physical properties

The unique luster of pearls depends upon the reflection, refraction, and diffraction of light from the translucent layers. The thinner and more numerous the layers in the pearl, the finer the luster. The iridescence that pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. In addition, pearls (especially cultured freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or black. The very best pearls have a metallic mirror-like luster.
Because pearls are made primarily of calcium carbonate, they can be dissolved in vinegar. Calcium carbonate is susceptible to even a weak acid solution because the crystals of calcium carbonate react with the acetic acid in the vinegar to form calcium acetate and carbon dioxide.

Identifying Pearl

Pearls can be identified by their pearly lustre and when rubbed gently against the teeth, a slightly rough surface texture can be detected, whereas imitation pearls feel smooth. The surface appearance of natural and cultured pearls is the same, but the density of cultured pearls is usually higher, at approximately 2.73 for most. The only definite way of distinguishing between natural and cultured pearls is to examine their internal structure. Experts use endoscopes to do this through the drill holes of pearls. Natural pearls have concentric internal layers.

Pearl: Origin and Gemstone Sources

Pearls are found and cultured in waters all over the world. Natural sea pearls are found in Australia, Japan, Central America, the Persian Gulf, the Gulf of Manaar (between India and Sri Lanka), the coast of Madagascar, Burma (Myanmar), the Philippines, the South Pacific Islands (including Tahiti and Fiji) and South America.
Natural river pearls are found in Asia, Europe and North America.
Cultured seawater pearl sources include Southeast Asia (such as Indonesia and the Philippines), Australia, China, French Polynesia, Japan, South Pacific Islands (including Tahiti and Fiji) and the Philippines.
Cultured freshwater pearl sources include China and Japan.
Basra pearls where basra moti in the Indian language, natural pearl gemstone which are found in the Indian Ocean are also called as basra pearls.

Freshwater and saltwater pearls

Freshwater and saltwater pearls may sometimes look quite similar, but they come from different sources.
Freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, but also in colder more temperate areas such as Scotland (where they are protected under law). Most freshwater cultured pearls sold today come from China.
Saltwater pearls grow within pearl oysters, family Pteriidae, which live in oceans. Saltwater pearl oysters are usually cultivated in protected lagoons or volcanic atolls.

Determining Pearl Gemstone Value

Pearl Colour

Pearls are available in a variety of colours. Colours of pearls include the following: White, pink, silver, cream, golden, green, blue and black. Some pearls exhibit iridescence, which is known as orient.

Pearl Clarity and Lustre

The lustre of pearls depends on the quality of the nacre. Pearls should have the characteristic shiny pearly lustre and their surface should show sharp and bright reflections. The surfaces of good quality pearls are smooth and blemish-free with a suitable layer of nacre to increase durability.

Pearl Cut and Shape

Pearls can be round, oval, pear-shaped or misshapen (baroque pearls). However, the best materials are regularly shaped. The most valuable shapes are symmetrical spheres or symmetrical drops. Pearl sizes depend on the type of mollusc that they form in and they typically range from 2 mm to 16 mm in diameter.

Pearl Treatment

Pearls are often bleached to lighten and enhance their colour. In this way, a uniform colour can be achieved for beaded necklaces.

Metaphysical properties of Pearls

Pearls symbolise Purity, Spiritual Transformation, Charity, Honesty, Wisdom and Integrity, all the best within us. Pearls provide a clear vehicle for the advancing states of wisdom, as well as a clean channel for receipt of spiritual guidance.
Pearls can stimulate your femininity and help with self acceptance. They lift your spirits and make you feel calm and beautiful. They remind us to walk with Dignity.
Pearls not only provide a mirror in which to see ourselves, but give us insight into how we appear to others.
The ragged, rough grain of sand, transformed over time slowly growing into a object of great value and beauty. With it's humble beginnings, Pearls symbolise innocence and a pure heart, and help us get in touch with the simple honest things of life.
Pearl grants to its wearer extraordinary foresight, protects him from risky commercial transactions and from evil eye. Pearl's magical properties depend on its colour: white Pearl brings freedom, brownish - wisdom, yellowish - wealth, greenish - happiness.
Pearl signifies faith, charity and innocence. It enhances personal integrity and helps to provide a focus to ones attention. Pearl symbolises purity and is known as a “stone of sincerity”. It brings truth to situations and loyalty to a “cause”. Inhibits boisterous behaviour.

Healing properties of Pearls

Pearls have been used throughout medical history to help treat disorders of the digestive tract, muscular systems and the skin. Powders and potions containing pearls have also been developed to aid in fertility, as well as in easing the discomforts of the birthing process. Many cultures and societies have made similar claims for this lustrous gem.
The Chinese, for example, have depended on the healing properties of the pearl for centuries. They have used it to treat everything from simple eye ailments to serious heart problems, bleeding, fever and indigestion. To this day, the Chinese still use pearl powder as a skin whitener and a cosmetic, as do many other people around the world. In fact, the pearl is widely considered to be effective in controlling the skin conditions rosacea and acne.
Pearls are considered to be very effective in treating health issues related to the stomach, heart and spleen. It calms the mind and prevents hysteria, promoting mental stability.It was believed that Pearl boosts sexual energy, strengthens visual acuity and heals ears diseases. It is beneficial for heart, lungs (against tuberculosis, asthma, chronic bronchitis), kidneys, urinary system and liver. Pearl possesses sedative and also laxative effect, neutralises poison, lowers acidity, It relieves conditions of bloating and biliousness.
Pearl increases fertility and eases childbirth. Pearl also raises sensuality. Pearl was believed to be the main ingredient of "immortality elixir".

Properties of Pearl gemstone

ColourWhite, Blue, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Multicolored
Hardness2.5 - 4.5
Crystal SystemAmorphous
Refractive Index1.52 - 1.69
SG2.6 - 2.8
TransparencyOpaque
Double Refraction.156
LusterPearly
CleavageNone
Mineral ClassCalcium carbonate and conchiolin (organic) combined with water