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The chemical formula of mineral Beryl is indicated by Be3Al2(SiO3)6 or Beryllium Aluminum Silicate. Beryl is actually a Silicate mineral. The name of the mineral species Beryl is derived from the Greek word beryllo, which means precious blue green color of seawater. Beryl has been considered as gemstone since prehistoric times. Beryl minerals are commonly associated with other interesting minerals such as quartz, tourmalines, euclase, micas, calcite, and some feldspar. Beryls are commonly used as gemstones and also as mineral specimens. Beryl contains the element beryllium, thus it is also used as source of beryllium. Treating the stone with oil can mask internal flaws in beryl gems. Unscrupulous dealers will often apply this treatment to a stone without informing the buyer.

 

            Mineral Beryl is considered as one of the most important gem mineral in the mineral world and most especially among serious mineral collectors. This remains true despite the fact that Beryl mineral is often regarded unknown to the general social public and even in the gemstone buying public. A pure Beryl mineral is colorless in appearance. This Beryl variety usually allows the whole constituent of white light to pass through making the mineral non-pleochroic even between crossed nicols of geological polarizing microscopes. If Beryl happens to appear in various colors or shades when viewed under a polarized microscope, this varied coloration is brought about by many impurities present in the chemical composition of mineral Beryl. These splendid color varieties of mineral Beryl make it an interesting gemstone, which exhibits splendid microscope images under gemological microscope. Without these fascinating colors and different shades exhibited by the mineral, Beryl would turn out to be a rather ordinary and unattractive gemstone with only average brilliance and fire when viewed with the aid of gemological microscopes. There are different names applied for the different color varieties of mineral Beryl. The green variety is called Emerald. This Beryl variety displays fascinating green color in transmitted light of gemological microscope. The green color exhibited is by minute amounts of chromium present in its chemical structure. The blue variety is called Aquamarine. This blue variety of Beryl displays splendid microscope image in transmitted light of polarized light microscope for geologists and also under gemological microscope. The greenish-yellow variety is called Heliodor. Its color is due to the presence of Fe O charge transfer and rarely due to Uranium. It has fantastic color display under gemological microscope. The pink variety is called Morganite. Its color is due to the presence of manganese (Mn). The colorless variety is called Goshenite. The red variety is simply called red beryl and the golden variety is also called golden beryl. Emerald and Aquamarine are the two varieties of Beryl mineral, which are regarded very popular in the gem world. All varieties are producing brilliant and marvelous images when viewed under gemological microscopes. The rest of the varieties mentioned are also used as gemstones but are not as well known.

 

            The highly prized Beryl mineral variety is the Emerald gemstone. It is one of the most valued gemstones in the gem world. The green color of Emerald is considered peerless and oftentimes, all other green colored gemstones are compared to the intensity of the Emerald stone. More often, Emerald mineral specimens are flawed with mineral inclusions and fractures, which are clearly seen when gem mineral is viewed under a polarizing light microscope for geologists. These flaws are actually considered as part of the Emerald’s character, which is very unlikely to that of the other gems. These flaws are considerably helpful for they are used to determine natural from synthetically produced stones. Emerald stones, even low grade, when cut as gems carry a high price in the mineral markets. This is why uncut specimens of emerald are considerably rare on the mineral market. True Emerald specimens in matrix are especially hard to find. Most commonly, those that are seen in the mineral markets sold with a highly inflated price that are in matrix form are fakes. These are actually the natural crystals of Emerald, which are glued into a host rock and then sold as in matrix specimen.

 

            Aquamarine, the blue variety of beryl is also considered popular in the gem world. Even though considered as a popular gem, Aquamarine does not command a high price. There are plenty of uncut Aquamarines and those that are cut as gems in the mineral markets. Both cut and uncut materials are found exhibiting interesting brilliant stone image under petrographic polarizing light microscopes. They can be found in a relatively expensive price but not as high as that of the Emeralds. Aquamarine in large crystals can be possibly found available in the open market. Perhaps, they can be regarded to represent the largest raw gemstone specimens.

 

            Mineral specimens of Beryl are commonly found in a variety of shades that includes blue to blue green, emerald green, red, greenish gold, yellow, colorless and pink in transmitted light of petrographic polarizing light microscope. Beryl has various impurities making the mineral appear in various shades and colors. Beryl mineral usually exhibits vitreous luster in reflected light of geological polarizing light microscope. This mineral usually exhibits little fire or brilliancy, and so its valuable characteristic commonly depends on its hardness, transparency and color. The cleavage of Beryl when its mineral specimen is evaluated between crossed nicols of geological microscope is commonly found imperfect in one direction. This imperfect basal cleavage can be also found visible under several adjustments on the aperture diaphragm of polarizing light microscope for mineralogists but are usually not seen in thin sections. The hardness measure for this mineral Beryl using the Mohs scale method usually gives values ranging from 7.5 to 8. When Beryl mineral specimen is evaluated with the aid of petrographic polarizing microscope used in the field of optical mineralogy, its fracture found is commonly conchoidal. The specific gravity measure for this mineral Beryl usually gives an approximate value ranging from 2.6 grams per cubic centimeters to 2.9 grams per cubic centimeters, which is commonly considered average. When Beryl mineral specimens are rubbed on a white streak plate, they usually leaves whiter streak.

             Beryl minerals are known to crystallize in the hexagonal system of crystal formation. In the filed of optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. Crystals are commonly found as transparent to translucent in appearance. Beryl minerals are commonly found in elongated crystals with hexagonal cross sections. Crystals may be found in columnar formations where individual crystals form columns. Crystal habits of mineral Beryl typically include the hexagonal prism terminated by pinacoid faces. Many different pyramidal faces often modify the terminations. This modification can sometimes produce a rounded termination, which appear in the rough shape of a used pencil eraser. It may also have its crystalline-coarse formation, where it occurs as well-formed coarse sized crystals. Crystals are usually prismatic in form where crystals are shaped like slender prisms. Faces of the large crystals of mineral Beryl are often found pitted and striated lengthwise and rough. Beryl crystals are also considered brittle. They are considered also conchoidal. This is a very brittle fracture producing small, conchoidal fragments.  

Mineral Beryl usually exhibits prominent pleochroism between crossed nicols of petrographic polarizing light microscope used in the field of optical mineralogy. Specimens of mineral Beryl are usually non-fluorescent in ultraviolet light. This mineral Beryl is a uniaxial negative figure. After several chemical evaluations, Beryl is found not radioactive mineral. It usually displays moderate surface relief when specimen is evaluated or viewed between crossed nicols of polarizing light microscope for mineralogists. Commonly, it has weak birefringence and usually exhibiting interference colors that are in shades of gray, white or straw of the first order. Longitudinal sections of mineral Beryl commonly have parallel extinction angles while those basal sections usually appear dark in all positions. The orientation of mineral Beryl crystals between crossed nicols of petrographic polarizing microscope is length-fast. The interference figure on basal sections commonly gives a negative uniaxial figure without rings. The cross may show a slight opening in certain areas.

 

            Mineral Beryl commonly occurs in veins. They are usually found forming in hydrothermal veins and in pegmatites. They can be also found with feldspar and quartz. Beryl is found most commonly in granitic pegmatites. It also occurs in mica schists in the Ural Mountains. Best field indicators of mineral Beryl commonly include hardness and color, crystal habit and lack of good cleavage. Mineral Beryl has notable occurrences in types of localities that include California, Brazil, Africa, and many other localities for other beryls. Some areas are also included like Brazil, Russia and Pakistan for aquamarine. Colombia and some African localities for emerald are also considered. Beryls can be also found in some European countries such as Germany, Austria and Ireland. Morganite can be found in Madagascar.



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Saturday, November 28th, 2009 at 10:20 am
Category:
The Silicates Mineral Class
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