_:n4eef093601aa405fbf5cdc3453de68c3xb0
<http://schema.org/description>
"Brittle mica, any member of the mica group of silicate minerals that has calcium instead of potassium or sodium. The calcium substitution increases the aluminum-to-silicon ratio that enhances hardness. This causes it to break instead of bend. Margarite and clintonite are examples of brittle micas."
<https://www.britannica.com/science/brittle-mica>