Magnesiocummingtonite is the

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

rich endmember of the

cummingtonite Cummingtonite ( ) is a metamorphic amphibole with the chemical composition , magnesium iron silicate hydroxide. Monoclinic cummingtonite is compositionally similar and polymorphic with orthorhombic anthophyllite, which is a much more common ...

grunerite Grunerite is a mineral of the amphibole group of minerals with formula Fe7 Si8 O22( OH)2. It is the iron endmember of the grunerite-cummingtonite series. It forms as fibrous, columnar or massive aggregates of crystals. The crystals are monoclini ...

series of the amphibole group of minerals, with the following composition: (Mg)₇Si₈O₂₂(OH)₂. Magnesiocummingtonite is considered to be an aptly named magnesium rich variety of the mineral

which has Fe²⁺ substituting for some of the Mg. Divalent

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

may also substitute for magnesium in the crystal structure. It may be difficult to distinguish cummingtonite from the Mg rich variety in hand specimens. However, the

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

and degree of attraction to a magnetic field increases with more Fe content.

References

Mineralienatlas - Magnesiocummingtonite
{{Refend Amphibole group