brittle mica

brittle mica

[¦brid·əl ′mī·kə]
(mineralogy)
Hydrous sodium, calcium, magnesium, and aluminum silicates; a group of more or less related minerals that resemble true micas but cleave to brittle flakes and contain calcium as the essential constituent.
References in periodicals archive ?
Trioctahedral brittle mica, clintonite, has unusually high content of [Al.
In the case of true micas these interlayer cations are usually univalent, whereas in brittle micas they are divalent.
We can distinguish between true micas and brittle micas.
True and brittle micas found in igneous and metamorphic rocks, hydrothermal alteration and ore deposits are described (interlayer-deficient micas are described in another volume, on clay minerals).