cummingtonite-grunerite series

mineralogy

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June 25, 2026

Quick Summary

The cummingtonite-grunerite series refers to an amphibole mineral composed of iron and magnesium silicates. It is found in metamorphic rocks. Its chemical formula is (Fe, Mg)₇Si₈O₂₂ (OH)₂. This mineral is isomorphous with anthophyllite. The name "cummingtonite" originates from Cummington, Massachusetts.12

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amphibole
Chemical composition
The monoclinic cummingtonite-grunerite series exists from about Fe₂Mg₂Si₈O₂₂(OH)₂ to Fe₇Si₈O₂₂(OH)₂. Intermediate amphibole compositions do not exist between anthophyllite and the tremolite-actinolite series. Compositional gaps also exist between the cummingtonite-grunerite series and other calcic amphiboles. Consequently,
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The monoclinic cummingtonite-grunerite series exists from about Fe₂Mg₂Si₈O₂₂(OH)₂ to Fe₇Si₈O₂₂(OH)₂. Intermediate amphibole compositions do not exist between anthophyllite and the tremolite-actinolite series. Compositional gaps also exist between the cummingtonite-grunerite series and other calcic amphiboles. Consequently,
Read More