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.

Saturday, 10 December 2016

Diopside

What is Diopside?

Diopside is a pyroxene mineral with a chemical composition of MgCaSi2O6. It occurs in igneous and metamorphic rocks at many locations around the world. Gem-quality crystals of diopside are faceted into attractive gemstones that are occasionally seen in commercial jewellery. Granular diopside can be easily cut and polished. When it has an attractive colour, it is sometimes used as an ornamental stone. Perhaps the most important use of diopside is its value as an indicator mineral in the search for diamonds. Trail-to-lode prospecting using diopside and other indicator minerals has found diamond deposits in Canada, the United States, Africa, and other locations. Diopside has potential uses in the glass and ceramics industries, but the mineral usually occurs in accumulations that are too small or impure for effective mining.

Geologic Occurrence of Diopside

The most common occurrence of diopside at Earth's surface is as a primary mineral in olivine-rich basalts and andesites. In these rocks it can be present in quantities of a few weight percent. Diopside also forms during contact metamorphism of limestones and dolomites. Most of the crystalline diopside used to cut faceted gems and the granular diopside used as ornamental stone occurs in these carbonate deposits. Diopside is much more abundant in Earth's mantle than at the surface. Evidence for this is diopside as a common mineral in ophiolites, and diopside as a common mineral in kimberlites and peridotites that were formed during deep-source volcanic eruptions.
A very nice specimen of Diopside from Minas Gerais Brazil
with a distinct crystal surface formation.

Diopside as a Diamond Indicator Mineral

Most diamonds found at or near Earth's surface were delivered from the mantle during deep-source volcanic eruptions. These diamonds occur in vertical igneous structures known as pipes, which are often composed of kimberlite or peridotite.
These pipes are difficult to locate. Their surface exposure is usually covered with soil and vegetation, and it might be only a few acres in size. The pipes are often found by searching soils and sediments for mineral grains that are characteristic of the pipe but absent in local surface materials. Small particles of chromium-rich diopside are bright green in colour, are often abundant in the pipes, and are easy to recognise in surface materials.
Geologists use these green diopside fragments to locate the pipes. They know that the fragments are liberated as the pipe weathers, then scattered by the actions of mass wasting, streams, and glaciers. When diopside fragments are discovered, the geologist knows that they originated up-slope, up-stream, or up-ice from the location in which they were found.
A trail of diopside fragments can lead the geologist to the pipe from which they were weathered. This activity, known as "trail-to-lode" prospecting, finds many diamond pipes and an even larger number of pipes without diamonds.
Note: It would be almost impossible to locate pipes by looking for diamonds. Diamonds make up such a small fraction of the overall rock in the pipe, and weathering debris from the pipe is then mixed into local rock debris. An exceptional pipe might contain a couple carats of diamond per ton!

Chrome Diopside

Some crystals of diopside contain enough chromium to give them a rich green colour. These can be cut into beautiful faceted stones, beads, and cabochons. The appearance of these stones is best when they are under two carats because the material is often dark or strongly saturated.
Chrome diopside is occasionally seen in commercial jewellery. It has a rich green colour that enables it to serve as an alternative gem for emerald at a significantly lower price. Diopside is rarely treated, unlike emerald which is often treated with various materials to seal and hide fractures.
One problem with chrome diopside is its durability. It has two directions of perfect cleavage and a Mohs hardness of only 5.5 to 6.5. This gives it a risk of being scratched or broken. The gem is best used in earrings, necklaces, brooches, and other items that will not be subjected to abrasion or impact.
Even though chrome diopside is very attractive, there are barriers to it becoming a popular gem that is widely seen in jewellery. First are the durability concerns described above; second is that the jewellery-buying public is not familiar with diopside; and, third is the fact that a reliable supply of commercial stones in calibrated sizes has not been developed.

Star Diopside

Some diopside crystals are filled with microscopic needle-shaped inclusions that occur in parallel alignment with the crystal structure of the mineral. This network of parallel inclusions is known as a "silk." When this diopside is cut en cabochon, the parallel needles of the silk can reflect light much like how light is reflected from a spool of silk thread.
A silk with one direction of needle alignment will produce chatoyance, also known as a cat's eye. Silk with two or three directions of needle alignment will produce asterism. Two directions produces a four-ray star, and three directions produces a six-ray star. For these phenomena to appear, the stone must be cut with the needles oriented parallel to the bottom of the stone, and the top of the cabochon must be symmetrically cut.
The mineral needles that form the silk are known in some instances to be magnetite. They are sometimes abundant enough to make the cut gems slightly magnetic. If you approach them slowly with a magnet, the gems will move before the magnet touches them. The needles in some non-magnetic gems are thought to be rutile or ilmenite.

Violane

Some diopside formed during the contact metamorphism of dolomite or limestone has a granular texture similar to marble. This material is known as "violane." It is often white, gray, light blue, lilac, or purple in colour. Violane accepts a bright polish and is sometimes used to make cabochons, beads, and ornamental items. Violane is a rare material in nature and almost never seen in commerce.

Diopside as an Industrial Mineral

Diopside has potential uses in ceramics, glass-making, biomaterials, nuclear waste immobilisation, and fuel cell technology. Unfortunately, natural diopside is rarely found in deposits that simultaneously have a size, purity, and location that allows economic mining. This makes synthetic diopside cost-competitive with diopside produced by mining.

Geographic Distribution of Diopside

Gem-quality chrome diopside and violane are mined in limited amounts in Siberia, Russia. Most of the chrome diopside used in jewellery today comes from a few locations in Siberia. Small occurrences of chrome diopside are also known in Austria, Brazil, Burma, Canada (Ontario and Quebec), Finland, India, Italy, Madagascar, Pakistan, South Africa, Sri Lanka, and the United States (New York), but none of them produce regularly or in significant quantities.

Properties of Diopside

Chemical FormulaCaMgSi2O6
CompositionCalcium magnesium silicate, often with some iron
Variable FormulaCa(Mg,Fe)Si2O6
ColourLight to dark green, gray, yellow, light blue, purple, and white. May also be green with thin white streaks running though a crystal. Rarely colorless or multicoloured.
StreakWhite to light green
Hardness5 - 6
Crystal SystemMonoclinic

Crystal Forms 
and Aggregates
Usually as single, short prismatic crystals. Crystals may also be somewhat elongated, and usually have good terminations. Also massive, grainy, columnar, bladed, radiating, fibrous, as cleavage fragments, and in disordered aggregates of elongated crystals. May also be in v-shaped penetration twins, and crystals from certain localities have partially hollow or dissolved etchings.
TransparencyTransparent to opaque
Specific Gravity3.3 - 3.6
LusterVitreous, dull
Cleavage1,2 - prismatic at cleavage angles of 87º and 93º (Characteristic of minerals in the pyroxene group). May also exhibit parting in one direction.
FractureUneven to splintery
TenacityBrittle
Other ID MarksWhite forms of Diopside are occasionally fluorescent.
In GroupSilicates; Inosilicates; Pyroxene Group
Striking FeaturesColour, cleavage angles, and localities
EnvironmentContact and regional metamorphic rocks in hornfels, and in skarn deposits of hydrothermal metamorphic rock.
Rock TypeMetamorphic
Popularity (1-4)2
Prevalence (1-3)2
Demand (1-3)1

Diaspore

What is Diaspore or diasporite?

Diaspore, also known as diasporite, empholite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, α-AlO(OH), crystallising in the orthorhombic system and isomorphous with goethite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the luster is markedly pearly in character. It is colourless or greyish-white, yellowish, sometimes violet in colour, and varies from translucent to transparent. It may be readily distinguished from other colourless transparent minerals with a perfect cleavage and pearly luster like mica, talc, brucite, and gypsum by its greater hardness of 6.5 - 7. The specific gravity is 3.4. When heated before the blowpipe it decrepitates violently, breaking up into white pearly scales.
The mineral occurs as an alteration product of corundum or emery and is found in granular limestone and other crystalline rocks. Well-developed crystals are found in the emery deposits of the Urals and at Chester, Massachusetts, and in kaolin at Schemnitz in Hungary. If obtainable in large quantity, it would be of economic importance as a source of aluminium.
Diaspore, along with gibbsite and boehmite, is a major component of the aluminium ore bauxite.
It was first described in 1801 for an occurrence in Mramorsk Zavod, Sverdlovskaya Oblast, Middle Urals, Russia. The name, which was coined by René Just Haüy, is from the Greek for διασπείρειν, to scatter, in allusion to its decrepitation on heating.
Csarite, ottomanite, and zultanite are trade names for gem-quality diaspore (also known as Turkish diaspore) from the İlbir Mountains of southwest Turkey.

History and Occurrence

Diaspore as a mineral has been around since its discovery as a species in 1801, but it wasn't until the 1970's that this mineral was first faceted for gemstone use. From the 1970's through 2005 occasional gems were cut from Diaspore for collectors, but in 2006 this mineral started being mined specifically for gemstone use. Though Diaspore is found in several localities throughout the world, the only source of gemstone material is in a Bauxite deposit in the Anatolian Mountains of central Turkey. Originally exploited for its economic importance for the extraction of aluminium, this deposit is now solely mined for the production of this gemstone.
Diaspore is beautiful and exotic in a soft, subtle manner. It is also one of the lesser known of the colour-change gemstones. Some of the finest examples of gem quality diaspore are found in Turkey's Anatolian Mountains, but it can be found in numerous places around the globe. A rising star in fine jewellery, it's easy to fall in love with its sparklingly brilliant, tranquil earthy colours.

Properties of Diaspore

Chemical FormulaAlO(OH)
ColourRed, Green, Yellow, Pink
Hardness6.5 - 7
Crystal SystemOrthorhombic
Refractive Index1.70 - 1.75
SG3.3 - 3.5
TransparencyTransparent
Double Refraction0.048
LusterVitreous
Cleavage1,2;2,1
Mineral ClassDiaspore

Diamond

What is Diamond?

Diamond, the most famed and fabled of all gemstones, is very unique in many ways. Renowned for being the hardest substance on earth, its sparkling fire, durability, and rarity make Diamond the most prize of all gems. No gemstone contains as much allure and interest as does Diamond.
Most Diamonds used as gemstones are colourless or very faintly coloured. However, coloured Diamonds, known as "fancies", can be extremely rare and valuable, and the most valuable gemstones ever known have been fancy Diamonds. In fact, fancy Diamonds are the most valuable substances known to man, with vivid coloured Diamonds historically being sold for more than a million dollars per carat!
A diamond is one of the best-known and most sought-after gemstones. Diamonds have been known to mankind and used as decorative items since ancient times; some of the earliest references can be traced to India.
The hardness of diamond and its high dispersion of light giving the diamond its characteristic "fire" make it useful for industrial applications and desirable as jewellery. Diamonds are such a highly traded commodity that multiple organisations have been created for grading and certifying them based on the four Cs, which are colour, cut, clarity, and carat. Other characteristics, such as presence or lack of fluorescence, also affect the desirability and thus the value of a diamond used for jewellery.
The most famous use of the diamond in jewellery is in engagement rings. The practice is documented among European aristocracy as early as the 15th century, though ruby and sapphire were more desirable gemstones. The modern popularity of diamonds was largely created by De Beers Consolidated Mines Ltd., which established the first large-scale diamonds mines in South Africa. Through an advertising campaign beginning in the 1930s and continuing into the mid-20th century, De Beers made diamonds into a key part of the betrothal process and a coveted symbol of status. The diamond's high value has been the driving force behind dictators and revolutionary entities, especially in Africa, using slave and child labour to mine blood diamonds to fund conflicts. Though popularly believed to derive its value from its rarity, gem-quality diamonds are quite common compared to rare gemstones such as Alexandrite, and annual global rough diamond production is estimated to be about 130 million carats (26 tonnes). The value of diamonds is attributed largely to the industry's tight control over this supply.

Gemological characteristics

The most familiar usage of diamonds today is as gemstones used for adornment, a usage which dates back into antiquity. The dispersion of white light into spectral colours is the primary gemological characteristic of gem diamonds. In the twentieth century, gemologists have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics known informally as the four Cs are now commonly used as the basic descriptors of diamonds: carat, cut, colour, and clarity. This system was developed by Gemological Institute of America in 1953 as internationally recognised standard to evaluate diamonds characteristics.
Most gem diamonds are traded on the wholesale market based on single values for each of the four Cs; for example knowing that a diamond is rated as 1.5 carats (300 mg), VS2 clarity, F colour, excellent cut round brilliant, is enough to reasonably establish an expected price range. More detailed information from within each characteristic is used to determine actual market value for individual stones. Consumers who purchase individual diamonds are often advised to use the four Cs to pick the diamond that is "right" for them.
Other characteristics also influence the value and appearance of a gem diamond. These include physical characteristics such as the presence of fluorescence as well as the diamond's source and which gemological institute evaluated the diamond. Cleanliness also dramatically affects a diamond's beauty.

Properties of Diamond
Raw Diamond,

Chemical FormulaC
ColourColorless, Blue, Red, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black
Hardness10
Crystal SystemIsometric
Refractive Index2.417 - 2.419
SG3.1 - 3.5
TransparencyTransparent to opaque
Double RefractionNone
LusterAdamantine
Cleavage1, all sides - octahedral. Dodecahedral Diamonds and Borts exhibit poor cleavage or no cleavage at all.
Mineral ClassDiamond

Danburite

What is Danburite?

Danburite is one of the least known of the colourless gems, though it makes a very good jewellery stone. It is a calcium aluminium borate silicate by chemical composition and is quite a hard material, with a rating of 7 on the Mohs scale. Since it has a moderately high refractive index (about the same as tourmaline) danburite can can be faceted with good results.
Danburite is primarily a collectors gemstone. It is usually colourless; yellow and light pink gems are seldom cut. Danburite is named after the city of Danbury, Connecticut, where this mineral was first described, though no gem grade material has come from Danbury. Danburite has good hardness and facets well, but its lack of fire in colourless stones limits its use as a mainstream gemstone.

History and Occurrence

In 1839 American mineralogist Charles Upham Shephard discovered a clear, bright, colourless gemstone in Danbury, Connecticut, and named it danburite after the location. Unfortunately for danburite, it was discovered at a time when coloured gemstones were heavily promoted and highly desired. This colourless find, therefore, didn't create much excitement at that time. Danburite, which belongs to a class of minerals known as silicates, remained relatively unknown for years, but is steadily growing in popularity today.

Properties of Danburite

Yellow Danburite
Chemical FormulaCaB2Si2O8
ColourColourless, Yellow, Pink
Hardness7
Crystal SystemOrthorhombic
Refractive Index1.63
SG2.9 - 3.0
TransparencyTransparent
Double Refraction-.007
LusterVitreous
Cleavage1,1
Mineral ClassDanburite

Coral

What is Coral?

Precious coral or red coral is the common name given to Corallium rubrum and several related species of marine coral. The distinguishing characteristic of precious corals is their durable and intensely coloured red or pink skeleton, which is used for making jewellery.
Coral is not a mined stone or mineral, but an organic gemstone. It is the hardened, skeleton-shaped result of secretions continuously deposited by marine polyps. It looks like a colourful underwater plant, but it is actually a priceless gift from the sea.

Habitat

Coral is found in clear at between 15 and 160 feet. The greater the depth, the lighter the coral's colour. Coral reefs are found in almost all of the world's oceans. The biggest is the Great Barrier Reef, off the coast of Queensland, Australia.
Italian red coral is in the highest demand In the jewellery industry and is considered the finest quality. The finest specimens come from Sardinia (Italy) and Tunisia. Coral from Japan and China is considered slightly inferior in quality, but it is more expensive than Italian red, because it is less abundant. Coral is also found off the coast of Washington State (U.S.A) and the Aleutian Islands off of Alaska.

Coral Gemstone

Unlike most other gemstones which are of mineral origin, Coral is organic, formed by living organisms. It forms from branching, antler-like structures created from coral polyps in tropical and subtropical ocean waters. When the coral polyps die, the hardened skeleton remains, and this material is what is used as a gemstone. Most coral is white, but nature can create coral in several other colours, including the popular orange to red forms. This Red Coral, or Precious Coral as it is often known by, is the most used gemstone form of Coral. In fact, the colour known as coral is derived from the typical pinkish-orange colour of many red Coral gemstones.
The hard skeleton of red coral branches is naturally matte, but can be polished to a glassy shine. It exhibits a range of warm reddish pink colours from pale pink to deep red; the word coral is also used to name such colours. Owing to its intense and permanent coloration and glossiness, precious coral skeletons have been harvested since antiquity for decorative use. Coral jewellery has been found in ancient Egyptian and prehistoric European burials, and continues to be made to the present day. It was especially popular during the Victorian age.
Precious coral has relative density of 3.86 and hardness 3.5 on the Mohs scale. Due to its softness and opacity, coral is usually cut en cabochon, or used to make beads.
Coral is typically worn in pieces that weigh at least three carats. A ring or pendant can hold a piece weighing up to twelve carats. Red coral may be set in gold or silver.

Properties of Coral Gemstone

Chemical FormulaMostly calcium carbonate
ColourWhite, Red, Orange, Pink, Gray, Black
Hardness3 - 4
Crystal SystemAmorphous
Refractive Index1.48 - 1.65
SG2.6 - 2.7
TransparencyTranslucent to opaque
Double Refraction-.172
LusterVitreous, waxy
CleavageNone

Copper

What is Copper?

Copper is a chemical element with symbol Cu (from Latin: cuprum) and atomic number 29. It is a soft, malleable and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a reddish-orange colour. It is used as a conductor of heat and electricity, as a building material and as a constituent of various metal alloys, such as sterling silver used in jewellery, cupronickel used to make marine hardware and coins and constantan used in strain gauges and thermocouples for temperature measurement.
Copper is found as a pure metal in nature, and this was the first source of the metal to be used by humans, c. 8000 BC. It was the first metal to be smelted from its ore, c. 5000 BC, the first metal to be cast into a shape in a mold, c. 4000 BC and the first metal to be purposefully alloyed with another metal, tin, to create bronze, c. 3,500 BC.
In the Roman era, copper was principally mined on Cyprus, the origin of the name of the metal, from aes сyprium (metal of Cyprus), later corrupted to сuprum, from which the words copper (English), cuivre (French), Koper (Dutch) and Kupfer (German) are all derived. The commonly encountered compounds are copper(II) salts, which often impart blue or green colours to such minerals as azurite, malachite, and turquoise, and have been used widely and historically as pigments. Architectural structures built with copper (usually roofing elements) corrode to give green verdigris (or patina). Decorative art prominently features copper, both in the elemental metal and in compounds as pigments. Copper compounds are also used as bacteriostatic agents, fungicides, and wood preservatives.
Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustaceans copper is a constituent of the blood pigment hemocyanin, replaced by the iron-complex haemoglobin in fish and other vertebrates. In humans, copper is found mainly in the liver, muscle, and bone. The adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. Hence a healthy human weighing 60 kilogram contains approximately 0.1 g of copper. However, this small amount is essential to the overall human well-being.

Characteristics

Physical

Copper, silver and gold are in group 11 of the periodic table, and they share certain attributes: they have one s-orbital electron on top of a filled d-electron shell and are characterised by high ductility and electrical and thermal conductivity. The filled d-shells in these elements contribute little to interatomic interactions, which are dominated by the s-electrons through metallic bonds. Unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper. At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is usually supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms.
The softness of copper partly explains its high electrical conductivity (59.6×106 S/m) and high thermal conductivity, the second highest (second only to silver) among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature originates primarily from scattering of electrons on thermal vibrations of the lattice, which are relatively weak in a soft metal. The maximum permissible current density of copper in open air is approximately 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively.
Copper is one of four metallic elements with a natural colour other than gray or silver, the others being caesium (yellow), gold (yellow), and osmium (bluish). Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic colour of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells corresponds to orange light. The same mechanism causes the yellow colour of gold and caesium.
As with other metals, if copper is put in contact with another metal, galvanic corrosion will occur.

Chemical

Copper does not react with water but it does slowly react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion (passivation). A green layer of verdigris (copper carbonate) can often be seen on old copper structures, such as the roofing of many older buildings and the Statue of Liberty. Copper tarnishes when exposed to some sulphur compounds, with which it reacts to form various copper sulphides.

Isotopes

There are 29 isotopes of copper. 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper; both have a spin of  3⁄2. The other isotopes are radioactive, with the most stable being 67Cu with a half-life of 61.83 hours.Seven metastable isotopes have been characterised; 68Cu is the longest-lived with a half-life of 3.8 minutes. Isotopes with a mass number above 64 decay by β−, whereas those with a mass number below 64 decay by β+. 64Cu, which has a half-life of 12.7 hours, decays both ways.
62Cu and 64Cu have significant applications. 62Cu is used in 62Cu-PTSM as a radioactive tracer for positron emission tomography.

Occurrence

Copper is produced in massive stars and is present in the Earth's crust in a proportion of about 50 parts per million (ppm). It occurs as native copper, in the copper sulphides chalcopyrite and chalcocite, in the copper carbonates azurite and malachite, and in the copper(I) oxide mineral cuprite. The largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal, with the largest single crystal ever described measuring 4.4×3.2×3.2 cm.

Physical Properties

Chemical FormulaCu
ColourMetallic, Red, Orange, Brown
Hardness2.5 - 3
Crystal SystemIsometric
SG8.9
TransparencyOpaque
Double RefractionNone
LusterMetallic
CleavageNone
Mineral ClassCopper

Friday, 9 December 2016

Citrine Gemstone

What is Citrine?

Citrine is the yellow to orange variety of Quartz. Natural Citrine is not common; most Citrine on the gem market is produced by heat treating Amethyst and Smoky Quartz. It takes a relatively low temperature to change the colour light to golden yellow, and heating to higher temperatures will give the stone a darker yellow to brownish-red colour. The name Citrine is derived from the citron fruit, a yellow fruit similar to the lemon. (In fact, citron means "lemon" in several languages).

Citrine Colour

Citrine is sometimes very pale or almost colourless. Among deeper coloured stones may be seen wine-yellow, honey-yellow, and saffron-yellow specimens, while others have quite a pronounced brown tinge. Stones of a deep brownish-yellow colour are very similar to topaz, and those of a fine golden-yellow are quite equal in beauty to yellow topaz and can scarcely be distinguished on mere inspection from latter stone except by an expert. 

Citrine Gemstone

Natural citrines are rare. Most commercial citrine is heat-treated amethyst or smoky quartz. Because the colour is now caused by finely distributed iron minerals (mostly hematite and goethite), heated amethyst is not a citrine in the strict sense. Quartz coloured by inclusions of any kind is not called a citrine.

History

Citrine is a transparent, yellow variety of Quartz, ranging in colour from pale to golden yellow, honey or almost brown, and may contain rainbow or sparkle inclusions. The name comes from the French word citron, meaning lemon. It was used as a gem in Greece as far back as 300 B.C., and because of its colour, is sometimes mistakenly referred to as Gold Topaz, Madeira or Spanish Topaz, or Safranite. Much of the commercial Citrine on the market is heat-treated Amethyst or Smoky Quartz that produces an enhanced Citrine colour, usually a deeper amber or orange-reddish shade. Most Natural Citrine is a pale yellow colour.

Properties of Citrine

Chemical FormulaSiO2
ColourYellow, Orange, Brown
Hardness7
Crystal SystemHexagonal
Refractive Index1.54 - 1.55
SG2.63 - 2.65
TransparencyTransparent
Double Refraction.009
LusterVitreous
CleavageIndiscernible
Mineral ClassQuartz