Crystal Symmetry Of Aquamarine
by Greg Williams/science Photo Library
Title
Crystal Symmetry Of Aquamarine
Artist
Greg Williams/science Photo Library
Medium
Photograph - Photograph
Description
Crystal symmetry of aquamarine, illustration. Aquamarine is a variety of beryl, a mineral built around 12-membered crown-shaped rings of six tetrahedral silicon atoms alternating with six bridging oxygen atoms (lightest blue). Each silicon atom is also bonded to two other oxygen atoms that are shared with beryllium(2+) and aluminium(3+) cations. These metal ions form a second ring that encloses the first. The outer ring has six aluminium oxide (AlO6) octahedra (dark blue) alternating with six tetrahedral beryllium oxides (BeO4) groups. The rings create channels that contain Group 1 cations, caesium(+) (larger) and sodium(+) (darker). Pure beryl is colourless, but trace amounts of impurities give coloured gemstones. Aquamarine, is a pale blue form of beryl contaminated with iron(2+) in some of the aluminium(3+) sites. The green emerald has chromium(3+) impurities; iron(3+) impurities give heliodor, a golden form of beryl, and morganite is pink due to manganese(2+).
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October 23rd, 2019
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