[crazycoffey]

Beryllium is a constituent of about 30 identified minerals, but most are rare. The most common beryllium mineral by far is beryl, 3BeO·Al2O3·6SiO2. This is a hard (Mohs 7.5-8.0), relatively light (spgr 2.75-2.80) found in granitic rocks, pegmatites, mica schists and similar environments, occasionally in huge crystals. One crystal was 9 m in length, and weighed 25 tons. Beryl is typically full of inclusions, milky but translucent, and of a greenish color. Clear crystals, which are much smaller but can still be of considerable size, are valuable gemstones. Pure beryl is clear and transparent, but small amounts of impurities color it very attractively. Aquamarine is a fine, pale green-blue, while emerald is deep green due to Cr+++ ion. Because of its color, emerald is the most expensive gemstone, sometimes more costly than diamond. Since the index of refraction of beryl is only 1.580, not much different from that of glass, it does not have the fire or brilliance of diamond and similar gems. However, it is very hard (only corundum, 9, and diamond, 10) are harder. Morganite, a pink to rose beryl, and Golden Beryl, a golden-yellow gem, are less costly than emerald and aquamarine. Usually, the crystals are hand-picked to separate them from the gangue. In ancient times, precious green gems were called smaragdos. This term was applied not only to emerald, but also to malachite.Currently, most beryllium (93% of world output in 2000) comes from a bertrandite deposit in Juab County, Utah, in Spor Mountain. Bertrandite is Be4Si2O7(OH)2, an alteration product of beryl. It forms clear or white orthorhombic crystals with one plane of good cleavage, is hard (6-7) and of moderate weight (sp.gr. 3.3-3.5; one source says 2.6). The concentrate is sent to Ohio for processing.Perhaps the most important beryllium mineral after beryl and bertrandite is chrysoberyl, Be(AlO2)2, which at 8.5 is nearly as hard as corundum. Its crystals are orthorhombic, often occurring in pseudo-hexagonal clusters. When of gem quality, chrysoberyl provides alexandrite, with its amazing dichroism, that makes it red when seen from one direction, green from another, and also cat's eye, with inclusions of rutile (TiO2). Another rare beryllium mineral is euclase, named after its perfect cleavage. Its formula is BeAlSiO4(OH). It is a phyllosilicate (layered, like mica; beryl is a 3D tectosilicate), found in granite pegmatites, often with topaz. Due to its hardness (7.5) and durability, it is also found in placers. It may be clear, green or blue.