The finer varieties of beryl, which are transparent and of beautiful color, are distinguished as precious beryl, and are sometimes called aquamarine. These occur in crystals similar in form to those of emerald; but the regular hexagonal prism is more frequently modified by truncation on the angles or edges, acumination (sharpening to a point), etc. The prisms are often long with sides that are striated, often deeply so; but the truncating or terminating planes are smooth. The coarser varieties of beryl (common beryl) are also found crystallized, but often massive.
Beryl occurs chiefly as hexagonal crystals in veins that traverse granite or gneiss, or are embedded in granite; sometimes it is found in alluvial soils formed from those rocks. Hardness 8; relative density 2.6–2.8; melting point 1,400°C.
Related category GEOLOGY AND PLANETARY SCIENCE
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