[Chemical composition] beryl may contain some Na, K, Li, Cs, Rb , alkali metal. The alkali metal content is related to the metasomatism. [Crystal structure] hexagonal crystal system; Figure G-21 The crystal structure of beryl in (a) (0001) and (b) (10) Figure G-22 Crystal form of beryl [Form] The crystals are mostly long columnar, and the alkali-rich crystals are short columnar (Fig. G-22), or develop into a plate shape along {0001}. There are often parallel c-axis stripes on the cylinder surface, and the alkali-free stripe is more pronounced than the alkali-containing beryl cylinder. Physical Properties] pure beryl is colorless and transparent, common colors are green, yellow-green, pink, dark green, fresh, deep blue sea-blue gem say that blue is caused by Fe 2+, green green Called emerald, is a very precious gem, its color is caused by Cr 2 O 3 , in addition, Cs is pink, a small amount of Fe 2 O 3 and Cl is yellow green; glass luster; transparent to translucent . The cleavage is not complete. Hardness 7.5 ~ 8. The relative density is 2.6 to 2.9. [genesis and occurrence] beryl is mainly produced in granitic pegmatite, yunyingyan and high temperature hydrothermal veins. The beryl is produced in the granitic pegmatites of Inner Mongolia, Xinjiang, and Northeast China. In pegmatite were not accountable, beryl composition substantially free of alkali, often coexist with quartz, potassium feldspar, feldspar, white mica. The beryl formed by the late sodium metabolization has a base content of up to 7.23%. This beryl is often symbiotic with minerals such as albite, spodumene , quartz and muscovite. [Identification characteristics] It is easy to identify according to crystal form and hardness and cleavage is not developed. [Main use] is an important ore mineral of Be. Beautiful and transparent, it can be used as a high-grade gem material. Among them, emerald is the best, and its processed value is no less than diamond.
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a 0 = 0.921 nm, c 0 = 0.917 nm; Z = 2. The beryl crystal structure is arranged in parallel with the vertical c-axis of the hexagonal ring composed of [SiO 4 ] tetrahedron, and the upper and lower rings are shifted by 25°, and are connected by Al 3+ and Be 2+ ;; the Al 3+ coordination number is 6, The Be 2+ coordination number is 4, which is distributed on the outer side of the ring, so there are wide channels parallel to the c-axis at the center of the ring to accommodate large-radius ions K + , Na + , Cs + , Rb+ + and water molecules (Fig. G-21). 0) projection on the surface 
Beryl
Be 3 Al 2 [Si 6 O 18 ]