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 ?
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).