Beryl

Article By:

Barton, Mark D. Department of Earth and Space Sciences, University of California, Los Angeles, California.

Last reviewed:February 2021

DOI:https://doi.org/10.1036/1097-8542.079600

Show previous versions

• Beryl, published October 2019:Download PDF Get Adobe Acrobat Reader

The most common beryllium mineral. Beryl, Al₂[Be₃Si₆O₁₈], crystallizes in the hexagonal system with space group P6/mcc. The crystal structure consists of six-membered rings of corner-sharing silicon-oxygen (SiO₄) tetrahedra cross-linked by corner-sharing beryllium-oxygen (BeO₄) tetrahedra to make a three-dimensional honeycomb structure; aluminum-oxygen (AlO₆) octahedra lie between the Si₆O₁₈ rings. Cordierite, (Mg,Fe)₂[Al₄Si₅O₁₈], has a similar structure. Open channels parallel to the sixfold axis contain variable amounts of alkalies (up to 5–8 wt %), such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs), and water molecules (up to ∼2.5 wt %). Minor amounts of iron (Fe), chromium (Cr), manganese (Mn), and other metals substitute for aluminum, contributing to the various colors of natural beryl. Beryl has a vitreous luster and is typically white to bluish- or yellowish-green, but it can also be shades of yellow, blue, and pink (see illustration). Its hardness is 7.5–8 on Mohs scale; it has an imperfect basal cleavage and a specific gravity of 2.7–2.9 (increasing with alkali content). Weakly colored varieties can be confused with quartz or apatite. See also: Crystal structure; Hardness scales

The content above is only an excerpt.