Tuesday, February 28, 2012
Gems & Minerals of Pakistan. Rocks. Stone. Ruby. Peridot. Emerald. Sapphire. Issue Date 24-02-2012.
Special Postage Stamps on Gems And Minerals of Paksitan February 24, 2012:- Emerald:- Emerald, the name is of ancient origin, the Latin “Samaragdus” known as Green Stone, is a variety of the mineral beryl (Be3Al2(SiO3) 6) colored green by trace amounts of chromium and sometimes vanadium. It has hexagonal crystal system, having hardness of 7 – 8 in Moh scale.
The inclusion in emerald can be highly distinctive; bubbles of gas in a liquid (like a sprit level), within spindle-shaped or, more rarely, truncated prismatic cavities; birefringent, circular plates of mica; multifaceted pyrite crystals or calcite rhombohedra.
The typical color is beautiful due to traces of chromium in the crystal structure. An emerald has various shades from light or dark green to bright or leaf green. The most common shape for gem is the step or trap cut, which is also known as emerald cut. Stones of fine colour, weighing more than 2 carats, are among the most highly valued gemstones.
Unlike diamond, where the loupe standard, i.e. 10x magnification, is used to grade clarity, emerald is graded by eye. Thus, if an emerald has no visible inclusions to the eye (assuming normal visual acuity), it is considered flawless. Stones that lack surface breaking fissures are extremely rare and therefore almost all emeralds are treated, “oiled”, to enhance the apparent clarity.
In Pakistan, Emeralds are found at Mingora, Gujar Killi, Shamozai, Charbagh, Makhad of Swat; Gandao of Mohmand Agency, Barang of Bajaur Agency, Kot of Malakand Agency, khaltaro of the Gilgit Biltistan and Dokoo of Shinger Valley.
Rubby:- The name comes from the Latin rubrum, “red”. It is the most valuable variety of corundum group. Its crystal system is trigonal. Ruby is a-alumina (the most stable form of AI2O3) in which a small fraction of the aluminum3+ ions are replaced by chromium3+. This crystallographic arrangement strongly affects each Cr3+, resulting in light absorption in the yellow-green region of the spectrum and thus in the red color of the gem.
The brightest red and thus the most valuable rubies often have areas full of inclusions in the form of minute rutile neddles, which interfere with the light producing a distinctive silky shine known, in fact, as silk. When the silk is not heavy, the stones are clearer, more attractive and even more valuable. Other, mainly crystalline inclusions are normally found as well. Rubies of this type are not usually more than a few carats in weight. There are exceptions, generally containing copious inclusion and have hardness 9 in Moh scale.
The ruby is considered one of the four precious stones, together with the sapphire, the emerald, and the diamond.
The brightest and most valuable “red” called pigeon blood-red, commands a huge premium over other rubies of similar quality. After color follows clarity similar to diamonds, a clear stone will command premium, but a ruby without any needle-like rutile inclusions may indicate that the stone has been treated.
Some rubies show a 3-point or 6-point aster whereas, some rubies show a 3-point or 6-point asterism or “star”. These rubies are cut into cabochons to display the effect properly. This is one example where inclusions increase the value of a gemstone. Furthermore, rubies can show a change in color though this occurs very rarely as a “cat’s eye” effect. These rubies are cut into cabshon to display the effect properly.
In Pakistan and Azad Jammu & Kashmir (AJK) Rubies are found at Aliabad of Hunza Valley, Basal area of Naran, Astore of Gilgit Baltistan and also huge and best quality deposits are found in Nangimali and Batakundi.
Sapphire:- The name of this blue variety of corundum is probably derived from the Latin sapphires and Greek sapheiros. This is one of the two or three gem-varieties of corundum, with another one being the red or deep pink ruby. Trace amounts of other elements such as iron, titanium, or chromium can give corundum blue, yellow, pink, purple, orange, or greenish color. Pink-orange sapphires are also called padmaraga. Pure chromium is the distinct impurity of ribies. However, a combination of e.g. chromium and titanium can give sapphire a color distinct from red.
Although blue is the most well-known color, sapphires are made up of any color of corundum except for red. Sapphires may also be colorless, and they are also found in shades of gray and black having a trigonal crystal structure with a hardness 9 in Moh scale.
Inclusions are, as a rule, less obvious in very dark stones, due to their general lack of transparency, whereas medium to large pale stones often show distinct “veils” or “feathers” caused by very fine inclusion and foreign crystals, which are sometimes transparent, sometimes dark, submetallic, opaque, and, very occasionally, bright red.
In Pakistan Sapphire deposits are found in Aliabad and Muzaffarabad (AJK).
Peridot:- The name could be derived from the Greek “peridona” meaning “giving plenty” or from the Arabic word Faridat or Zabargad. Later the stone was known as Topazion. Probably around the 18th century, the French were the first to call the yellowish-green stone Peridot, although the English have similar claims, It was probably, regarding their history, more of a French name. However, the name source of the Peridot is not very clear.
It was discovered a couple of thousands years BC ago by the sailors landed on a small Island of the Serpents, red sea, under the bright moonlight they saw glowing crystals among the volcanic earth. At first light those crystals turn green glitters in the sand.
Peridot belongs to the forsterite-fayalite (most of the gem variety is predominantly foresterite, named after the German naturalist, John Forester) mineral series which is part of the Olivine group. It is one of the “idiochromatic” gems, meaning the color created by the basic chemical composition of the mineral itself, not from minor impurities, and therefore will only be found in shades of green.
Its chemical formula is (Mg,Fe)2SiO4 with hardness of 6.5-7 in Moh scale.
In iron-and magnesium-rich intrusive rocks it usually occurs as unhedral crystal; but in effusive rocks, such as basalts, it more often has a prismatic appearance. Peridot shades very from a yellowish (olive) green, a stronger, almost bottle green, or pale yellow tinged with green. It has unexceptional, vitreous luster, increasing its resemblance to olive oil.
In Pakistan Peridot occurs to the southeast of west Sapat Gali, and to the north of Rah Wali Sapat (Parla Sapat, Kaghan-Naran area) and to the west of Ratti Gatti (Kohistan area).
Paksitan Post is issuing a set of four special postage stamps of Rs. 8/- denomination in eacs desigen on Gems and Minerals of Pakistan on February 24, 2012.