BerylBeryl is a most alluring and popular mineral. It occurs in a diversity of colors, and has several important gemstone varieties. The green variety, Emerald, is one of the most precious gems. Only green Beryl with a deep green or emerald-green color is called Emerald; light green Beryl is considered either Heliodor or simply "Green Beryl").
Aquamarine, another important gemstone, is the greenish-blue to blue variety of Beryl. Green Beryl from certain localities can be heat treated to produce sky-blue Aquamarine. Other popular gem varieties of Beryl are the pink Morganite, and the yellow Heliodor and Golden Beryl. A deep red variety of Beryl, known as Red Beryl (or Bixbite) is extremely rare, and only comes from two localities in Utah. When in good specimens, Red Beryl commands an outstanding premium and is very difficult to obtain. Pure Beryl is colorless. However, a wide range of impurities cause the diverse amount of colors and many varieties. The green color in Emerald is usually caused by traces of the elementchromium, and the blue color of Aquamarine usually by iron. Beryl is naturally transparent, however inclusions and impurities may make it opaque. Allgemmy transparent varieties are highly valued, but the other forms of Beryl in opaque crystals are much more common. Some of the largest natural crystals known are of Beryl, with enormous crystals having been found in several pegmatite occurrences. http://www.minerals.net/mineral/beryl.aspx Tourmaline GroupTourmaline is not a single mineral, but a group of several closely related minerals. The three most well-known members are Elbaite, Schorl, and Dravite. Other lesser known members include Uvite, Liddicoatite and Buergerite. There are yet more members of the Tourmaline group, but these are extremely rare and not discussed in this guide.
Tourmaline is extremely popular among collectors and is a well-known gemstone. It is the most multicolored mineral type known, occurring in virtually every color of the spectrum. Individual stones are often multicolored and are unsurpassed in their beauty. The color of some Tourmaline can be enhanced through heat treatment. Some greenish stones can be made deep green, some brownish-red stones can be made red, and some light pink stones can be made colorless through heating. Tourmaline has many interesting optical properties. Many green and blue specimens are strongly pleochroic. When viewed through their vertical axis, such specimens appear darker in color than when seen through their horizontal axis. In other Tourmalines, the color may actually be different when viewed at different angles because of the pleochroism. Certain Tourmalines exhibit a cat's eye effect when polished into cabochons. Tourmaline is both pyroelectric and piezoelectric. If a specimen is put under a pressure or temperature change, it will generate an electrical charge. When this happens, dust particles become attached to the crystal ends. http://www.minerals.net/mineral/tourmaline.aspx |
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