Glauconite
Glauconite, or greensand, greenish iron-silicate mineral that resembles tiny flake-like particles or little lumps of clay. Large deposits have been found in Colorado, New Jersey, and Wisconsin. Glauconite is used as a water softener. Its natural content of silicate of potassium and iron makes it invaluable to geologists in dating rocks and fossils.
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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Ghibellines to Grand Prix