Piemontite
Al 1%, Ca 2%, Fe 1%, Mn 1%, Si 3%,

estimated elemental composition and molecular weight 
Minerals with the same name may vary widely in appearance and composition, and very few are >99% (reagent grade) pure.

Gram formula weight (molecular mass) = 302.17


Minerals may vary in elemental composition and impurity levels. The formula given is an approximation.
Wikipedia Page:

Piemontite
is defined with respect to the entities below:
The entities below are defined with respect to:
Piemontite
Mineral (generic)


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