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Did you know that? Part II

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#37. Chrysoprase



Chrysoprase, chrysophrase or chrysoprasus is a gemstone variety of chalcedony. It is a cryptocrystalline form of silica with traces of nickel. Its color may vary from apple-green to deep green. The darker varieties of chrysoprase are referred to as prase.

Chrysoprase is cryptocrystalline, which is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This characteristic distinguishes it from the other varieties of crystalline quartz which are transparent and form six-sided crystals.

Agate, Carnelian and Onyx are some members of the cryptocrystalline silica family. It is the attractive color of chrysoprase, rather than any pattern of markings, that makes it very desirable. The word chrysoprase is derived from from the Greek ‘chrysos’ meaning ‘gold’ and ‘prasinon’, meaning ‘green’.

Emerald owes its green color to the presence of chromium. But the green color of chrysoprase is due to the presence of traces of nickel compounds in form of very small inclusions. The nickel reportedly occurs as different silicates, like kerolite or pimelite.

Chrysoprase results from the deep weathering of rocks. In the Australian deposits, chrysoprase occurs as veins and nodules. Chrysoprase measures 6 – 7 on the Moh’s scale of hardness. It has a conchoidal fracture like flint.

Chrome chalcedony is very similar to chrysoprase but its color is due to the presence of chromium rather than nickel. The best known sources of chrysoprase are Queensland, Western Australia, Germany, Poland, Russia, Arizona, California and Brazil.
 
Who could resist this perfect apple green gemstone,

irregular in its shape but set in a perfectly fitting silver clasp??

Neither me nor Subha - I am sure !!! :)
 
What our people earlier have found out is called search results. What now the scientists are doing is only research. Hope you agree. I am at a loss to understand why nobody understands this ?
 
#38. Citrine


Quartz is an abundant mineral found on the earth’s crust. Many different varieties of quartz are semi-precious gemstones.

Throughout the world, varieties of quartz have been, since antiquity, the most commonly used minerals in the making of jewelry and hard stone carvings.

The most important distinction between the types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline (aggregates of crystals visible only under high magnification).

Pure quartz or rock crystal is colorless and varies from transparent to translucent. Citrine, Rose quartz, amethyst, smoky quartz and milky quartz are the colored varieties of quartz.

Citrine is a variety of quartz whose color ranges from a pale yellow to brown. Natural citrines are rare and most of the commercial citrines are heat-treated amethyst.

Citrine contains traces of Fe3+ and is rarely found naturally. The name is derived from the Latin word ‘citrina’ which means “yellow”.
 
#39. Clinohumite


Clinohumite, a magnesium silicate, is an uncommon member of the humite group. It is most commonly found as tiny indistinct grains.

Large clinohumite crystals are sought by collectors and are also fashioned into bright, yellow-orange gemstones. Pamir Mountains (Tajikistan) and Taymyr (Northern Siberia) are the two sources of gem quality clinohumite.

Clinohumite – a monoclinic mineral – is typically a dark to light brownish or orange – yellow in color. It resembles the hessonite variety. Clinohumite is usually granular, but may also be prismatic. Crystals are almost always small.

Clinohumite is brittle and has a hardness of 6. Its fracture is uneven and conchoidal. Clinohumite may vary from transparent to translucent. Its luster varies from a dull vitreous to resinous.

Under shortwave ultraviolet light, some clinohumite may fluoresce orange – yellow but there is no fluorescence under long wave UV rays.
 
#40. Color changing garnet



Color changing garnet is one of the rarest of all gemstones. It is both unique and interesting. Any gem that changes color is a rare find and is coveted by collectors. Garnets include almost every color and exhibit the widest variety of color changes in the gem world.

It is commonly said that garnets come in every color of the rainbow except blue. This is still true to some extent. But there are recent discoveries of color-change garnets that turn blue in an artificial light.

The color change can be intense and equal to the color change seen in the top quality alexandrite. In fact color change garnets can easily be mistaken for alexandrite. Some of the best color change garnets are from the deposit in Bekily, Southern Madagascar.

Color Change Garnets are very unusual. The change happens when the stone is put under two different types of light. In daylight a color change garnet may appear blue/green while under incandescent light it changes color to pink-red.

The price and demand of this gemstone varies according to its size and quality. Color, clarity and the degree of color change are all important factors in evaluating the grade of the Color Change Garnet.
 
#41. Cordierite (iolite)


Cordierite was discovered in 1813 and named after the famous French geologist Louis Cordier. As the transparent variety iolite, it is often used as a gemstone. The name “iolite” comes from the Greek word for ‘violet’.

Another old name is dichroite, a Greek word meaning “two-colored rock”. It refers to the strong Pleochroism exhibited by Cordierite.

Pleochroism is an optical phenomenon in which a substance appears to be of different colors when viewed from different angles, especially with polarized light.

Cordierite has also been called “water-sapphire” and “Vikings’ Compass” because of its usefulness in determining the direction of the sun on overcast days. The Vikings having used it for this purpose.

This works by determining the direction of polarization of the sky overhead. Light scattered by air molecules is polarized, and the direction of the polarization is at right angles to a line to the sun. So even when the sun’s disc is obscured by dense fog or lies just below the horizon this can be used.

Gem quality iolite varies in color from sapphire blue to blue violet and from yellowish gray to light blue as the light angle changes. Iolite is sometimes used as an inexpensive substitute for sapphire. It is much softer than sapphires.

Iolite is abundant in Australia (Northern Territory), Brazil, Burma, Canada (Yellowknife area of the Northwest Territories), India, Madagascar, Namibia, Sri Lanka, Tanzania and the United States (Connecticut).

The largest iolite crystal found weighed more than 24,000 carats, and was discovered in Wyoming, USA.
 
#42. Cymophane



Translucent yellowish chrysoberyl exhibiting chatoyance is called cymophane or cat’s eye. Cymophane is derived from the Greek words meaning ‘wave’ and ‘appearance’, with reference to the chatoyancy sometimes exhibited.

In this variety, microscopic linear cavities or needle thin inclusions of rutile occur. When their orientation is parallel to the base they produce a chatoyant effect exhibited as a single ray of light passing across the crystal.

This effect is best seen in gemstones cut in cabochon form. The color in yellow chrysoberyl is due to Fe3+ impurities.

Many other minerals like tourmaline, scapolite, corundum, spinel and quarts can form “cat’s eye” stones similar in appearance to cymophane.

These stones as known as “quartz cat’s eyes”, or “ruby cat’s eyes” etc. Only chatoyant chrysoberyl can be referred to as “cat’s eye” with no other designation.

Gems lacking the silky inclusions required to produce the cat’s eye effect are usually faceted. An alexandrite cat’s eye is a chrysoberyl cat’s eye that changes color.

Cat’s eye became very popular by the end of the 19th century. Until that time, cat’s eye had been present only in gem and mineral collections.

The popularity and the value of the stone increased so much that in the early 20th century the prices could go up as high as $8000 for a cut stone.
 
#43. Danburite



Danburite is a crystalline mineral similar to topaz. Its chemical formula is CaB2(SiO4)2. It is between 7 to 7.5 on Moh’s scale of hardness. The crystal form of this mineral is orthorhombic.

It is usually colorless like quartz. But it can also exist in white, pale yellow, yellowish-brown and pink colors. It typically occurs in contact with the metamorphic rocks.

This gemstone is named after Danbury, Connecticut, U. S. A where it was first discovered in by Charles Upham Shephard in the year 1839. Danburite’s original locality is now buried under the city of Danbury, Connecticut.

Danburite is not a well-known mineral but is fast becoming popular now. Danburite is loved by the collectors of perfectly transparent crystals. Quartz looks different from danburite.

Danburite has a diamond-shaped cross-section and wedge like termination. In contrast quartz has hexagonal cross section and pyramidal terminations.

Danburite can be transparent or translucent. Its luster is vitreous. Fractures are uneven and conchoidal. Quartz, feldspar, cassiterite, corundum, dolomite and fluorite are the associated minerals.

Danburite occurs in Danbury, Russel of USA, Mexico, Japan , Burma and Switzerland.
 
#44. Demantoid


...........

Demantoid is a member of the garnet group of minerals. It is a green gemstone variety of andradite, which is a garnet rich in calcium and iron. The chemical formula is Ca3Fe2(SiO4)3. The chromium substitution is the cause of the demantoid’s green color. Presence of Ferric iron is the cause of the yellow color in the stone.

Demantoid has two misnomers such as livine, and Uralian emerald. Since Demantoid is the green variety of andradite garnet, it is always primarily green in color. Its color shade ranges from a very strong yellowish green to the color of a fine emerald. Some stones have a brownish cast, which is due to the presence of iron.

The dispersion of a demantoid is unusually high, and this exhibits itself as a visible “fire” of rainbow-colored flashes of light. This effect becomes less noticeable due to the green color of the stone.

Demantoids are generally very small and the polished stones may weigh under 1 carat or 200 mg. Bigger stones over 2 carats or 400 mg are rare. Stones over 3 carats or 600 mg are very rare.

Stones with more intense green coloration are generally highly valued. But it is the lighter stone of yellowish green which displays substantially more fire. The choice of stone color or the fire emitted by it is entire personal.

Russian demantoid often contain inclusions of a type of asbestos. These inclusions are feathery golden threads which tend to curve and resemble the tail of a horse. Hence they are referred to as ‘horsetail inclusions’. The presence of such inclusions indicate a natural and genuine demantoid. Such gemstones become more valuable because of their horsetail inclusions.

The micro structure of demantoid is affected by the presence of the ‘horsetails’. The ‘horsetail’ typically originates at the center of the nodule and the fibers branch out and radiate towards the surface. The demantoid free from the horsetail inclusions displays flat crystal faces.
 
#45. Dendritic agate




Dendritic agate is an unusual and a very attractive whitish-gray or colorless variety of chalcedony. It has unique dendrites or markings resembling a tree or a fern. This name dendritic agate is used for this type of gemstone.

The dendrites found in the dendritic agate are the inclusions of iron or manganese which are usually brown or black in color. Though dendrites appear to be of organic nature due to their fern-like structure, they are actually inorganic.

They are formed at fine fracture surfaces through crystallization of weathered solutions of the neighboring rock.
The dendrite inclusions occur at various depths in the rough stone.

Dendritic agate can be very tricky to cut. The stone needs to be cut carefully to expose the most interesting patterns.

Nature's own crystal garden!!!
 
#46. Diamond



Diamond is derived from the ancient Greek word adámas meaning “unbreakable”. It is an allotrope of carbon in which the carbon atoms are arranged in a structure called the diamond lattice.

Though graphite is more stable than diamond, the rate of conversion from diamond to graphite is negligible. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms.

Diamond has the highest hardness as 10 on Moh’s scale. This is used in the major industrial application of diamond in cutting and polishing tools.

Diamond has remarkable optical characteristics. Because of its extremely rigid lattice, it can be contaminated only by very few types of impurities. Combined with wide transparency, this results in the clear, colorless appearance of most natural diamonds.

Small amount of boron makes the color of the diamond blue , nitrogen makes it yellow , defective lattice makes it brown, exposure to radiation makes it green, purple, pink, orange or red.

Diamond also has relatively high ability to disperse light of different colors. This is the cause of its characteristic luster. Diamond has been the most popular gemstone always.

Most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers (87 to 120 mi) in the mantle of the Earth. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years or 1/4 to 3/4 the age of the earth.

Diamonds are brought close to the Earth′s surface through deep volcanic eruptions. Diamonds can also be produced synthetically in a process which simulates the conditions in the Earth mantle.

Diamond hardness depends on its purity, crystalline perfection and orientation. The hardness is higher for flawless, pure crystals. The hardest diamonds can be scratched only by other diamonds.

The hardness of diamond makes it the most suitable for daily wear. Because it can be scratched only by another diamond, it maintains its polish extremely well. Small wonder that engagement rings and wedding rings are made of diamonds.
 
#47. Diopside


Diopside (MgCaSi2O6) is a monoclinic pyroxene mineral. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It measures 6 on Moh’s scale of hardness. It varies from transparent to translucent crystals.

Diopside of gemstone quality is found in two forms: the black star diopside and the chrome diopside in which chromium is present giving it a rich green color. Chrome diopside is relatively soft to scratch since its harness is only 5.5 to 6.5 on the Moh’s scale of hardness.

Violane is a variety of diopside rich in manganese and varies from violet to light blue color. Diopside derives its name from the Greek words ‘dis’, meaning “twice”, and òpsè meaning “face” with reference to the two ways of orienting the vertical prism. Diopside was first described around 1800.

Diopside based ceramics have potential applications in various technological areas. ‘Silceram’- a diopside based glass-ceramic was produced in 1980s from blast furnace slag and other waste products.

Diopside based ceramics and glass-ceramics have potential applications in the field of biomaterials, nuclear waste immobilization and sealing materials in solid oxide fuel cells.
 
#48. Dumortierite



Dumortierite is a fibrous variably colored mineral of Aluminium boro silicate or Al7BO3(SiO4)3O3. Dumortierite crystals are vitreous.

They may vary in color from brown, blue and green to rarer colors like pink and violet. Variation in color happens when aluminium is substituted by the other trivalent elements.

Its hardness is 7 on Moh’ s scale. Crystals exhibit pleochroism from red to blue and blue to violet. Pleochroism is an optical phenomenon in which a substance appears to be of different colors when observed at different angles, especially with a polarized light.

Dumortierite quartz is a blue colored quartz containing abundant dumortierite inclusions. Dumortierite was first described in 1881 for an occurrence in the Rhône-Alps of France. It was and named after the French paleontologist Eugene Dumortier (1803-1873).

Dumortierite is used in the manufacture of high grade porcelain. It is sometimes used as imitation lapis lazuli. All the naturally occurring blue quartz are translucent or opaque.

Dumortierite deposits are found in Madagascar, Mozambique, Namibia, Sri Lanka, India, France, Italy, Poland and Norway, Austria, Brazil, Canada and Russia.
 
#49. Emerald.
Emerald is a variety of the mineral beryl. It is colored green by traces of Chromium and Vanadium. Beryl has a hardness of 7.5–8 Moh’s scale of hardness. Most emeralds are very brittle.

Emeralds are graded using four basic parameters – the four Cs : Color, Cut, Clarity and Crystal.

Before the 20th century, jewelers used the term water as in “a gem of the finest water” to express the combination of two qualities, color and crystal.

Normally, in the grading of colored gemstones, color is by far the most important criterion.

However, in the grading of emerald, crystal is considered a close second. Both are necessary conditions. A fine emerald must possess not only a pure verdant green color but also a high degree of transparency to be considered a top gem.

In the 1960s the American jewelry industry changed the definition of ‘emerald’ to include the green vanadium-bearing beryl as emerald.
As a result, vanadium emeralds purchased as emeralds in the United States are not recognized as such in the UK and Europe.

In America, the distinction between traditional emeralds and the new vanadium kind is often reflected in the use of terms such as ‘Colombian Emerald.’

Emerald is a brittle gem. It tends to chip off easily. It is rarely flawless. Chromium-a hard white metal-causes its rich green color.

In ancient times powdered emerald was believed to cure fever and plague. Colombia is the chief source of finest emeralds.
 
#50. Fire Agate



Fire Agate, a variety of chalcedony is a semi-precious natural gemstone found only in certain areas of northern Mexico and the southwestern United States.

These areas were subjected to massive volcanic activity during the Tertiary Period. The fire agates were formed during this period of volcanism when hot water saturated with silica and iron oxide repeatedly filled cracks and bubbles in the surrounding rock.

Fire agates have beautiful iridescent rainbow colors, similar to opal. Its hardness on Moh’s scale is between 6.5 and 7. This prevents fading, cracking and scratching of the gemstone.

The vibrant iridescent rainbow colors found within fire agates are created by the Schiller effect as found in mother-of-pearl. It is caused by the alternating silica and iron oxide layers which diffract and allow the light to pass. This light forms colors known as fire due to interference.

There is no actual object inside the stone. This special effect arises from light interference within the micro structure layering of the gem.
 
#51. Fire Opal



The fire opal was named for its color. The color itself comes from fine traces of iron oxide. With a hardness between 6 and 6.5 on the Moh’s scale, fire opal requires a protective setting, when worn as a ring stone.

The warm fiery orange-red has a positive effect on the mind. It conveys a sensation of warmth, peace and harmony. The fire opal is the lucky stone of those born under the sign Aries.

The tolerance of the fire opal to extreme heat is poor. So also its resistance to acids, alkaline solutions and sharp objects. The opal may lose its moisture to become cloudy and cracked.

It should not be exposed to intense light over long periods. Wearing it helps it to maintain its water balance, using the moisture of the wearer’s skin and that of the air. Fire opals which have been worn a great deal can be polished again.

Play of color, body color and transparency are the three criteria which determine the price of a fire opal. The more transparency and ‘fire’ it has and the more intense its body color, the more valuable it becomes.

The rarest and the most valued is the intense red-orange fire opal from Mexico with its strong play of color. A higher value is placed on fine cabochons than on faceted fire opals.

These gems glow from orange to red. They impart people with a positive approach to life. Their fiery color gives us vigor and energy. They make us love life.
 
#52. Fluorite


Fluorite (also called fluorspar) is a composed of calcium fluoride. The word fluorite is derived from the Latin root fluo, meaning “to flow” . This mineral is used in smelting iron to decrease the viscosity of slags.

In 1852 fluorite gave its name to the phenomenon of fluorescence which is prominent in fluorites from certain locations, due to certain impurities in the crystal. Fluorite also gave the name to fluorine – its constitutive element.

Fluorite is a colorful mineral, both in visible and ultraviolet light, and the stone has ornamental uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels.

Optically clear transparent fluorite lenses have disperse very little. Fluorite lenses exhibit less chromatic aberration. Hence they are valuable in optical instruments like microscopes and telescopes. Fluorite optics are also usable in the far-ultraviolet range where conventional glasses are too absorbent for use.

Fluorite comes in a wide range of colors and has subsequently been dubbed “the most colorful mineral in the world”. The most common colors are purple, blue, green, yellow, or colorless.

Less common are pink, red, white, brown, black, and nearly every shade in between. Color zoning or banding is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the size of the color centers.

Natural fluorite mineral has ornamental uses. Fluorite may be drilled into beads and used in jewelry. Due to its relative softness it is not widely used as a semiprecious stone.
 
#53. Goshenite



Colorless beryl is called goshenite. The name originates from the place where it was originally discovered. Since all these color varieties are caused by impurities and pure beryl is colorless, we might be tempted to assume that goshenite is the purest variety of beryl. But it is not.

Goshenite is found to some extent in almost all beryl localities. In the past goshenite was used for manufacturing eyeglasses and lenses owing to its transparency. Now it is used as a gemstone.

The gem value of goshenite is relatively low. However, goshenite can be colored yellow, green, pink, blue and in intermediate colors by irradiating it with high-energy particles. The resulting color depends on the content of impurities.

 
To spread out the articles here and in the thread

Dainty Dose of Delightful Information,

in future the articles on crystals will appear

in this thread only on the even days of the month

like 2nd, 4th, 6th .....30th of every month!

The next article will appear on 2-2-2013.
 
[h=1]#54. Grossularite[/h]

Grossular or grossularite is a calcium aluminium mineral species of the garnet group. Ferrous iron may replace a part of the calcium and ferric iron may replace a part of the aluminium.


The name grossular is derived from ‘grossularia’ the botanical name of gooseberry. It refers to the green garnet from Siberia. The other colors are yellow, red and cinnamon brown.


The more common variety of grossular is called hessonite. These yellow crystal appear similar to Zircon. But the hardness of hessonite is less than that of Zircon. The word hessonite itself means ‘inferior’


Green Grossular Garnet from Kenya and Tanzania is much sought after. Its name tsavorite is derived from Tsavo area of Kenya where this garnet was discovered in 1960s. Viluite, a variety of grossular, is usually olive green or brownish or reddish in color.


Grossular is known by other names such as colophonite, ernite, gooseberry-garnet etc. Some of the misnomers are South African jade, garnet jade, Transvaal jade, and African jade.
 
[h=1]#55. Hambergite[/h]
Hambergite (Be2BO3OH) is a beryllium borate mineral. It is named after the Swedish explorer and mineralogist Axel Hamberg. The mineral occurs as white or colorless crystals.

Hambergite occurs in beryllium bearing granite pegmatites as a rare accessory phase. Beryl, apatite, danburite, zircon, fluorite feldspar and quartz are some of the minerals it is associated with.


It was first described in 1890 by the mineralogist and geographer W.C.Brogger.
 
#56. Hematite


Hematite / Haematite, (Fe2O3) is the mineral form of iron oxide, one of several iron oxides. Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It is the main ore of iron.

Varieties include kidney ore, iron rose and specular hematite. The forms of hematite vary, but they all have a rust-red streak. Hematite is harder and more brittle than pure iron.

Huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places where there has been standing water or mineral hot springs.

The mineral can precipitate and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water as the result of volcanic activity.

Hematite’s popularity in jewelry was at its highest during the Victorian era in Europe. It has become popular in the western part of U.S.A. Certain types of hematite or iron oxide rich clay,have been used in gliding.

Hematite is used in art such as intaglio engraved gems. A synthetic material hematine is sold as magnetic hematite.
 
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