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The concentration of naturally occurring beryllium is variable. The average concentration in soil is about 6 parts per million (ppm), with a range of 0.1--42 ppm; humus soils show a concentration above the crustal average. The presence of beryllium in other geological materials shows similar variability: sandstones and limestones have a low concentration (<1 ppm), igneous rocks and shales a higher concentration (about 3 ppm). Beryllium ores may have a substantially higher concentration. For more details, see Wilbur (1980) and Rossman (1991), listed in Section 6.3.
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