One type of these minerals is a lithium source, lepidolite, and another has a chromium-rich variant called fuchsite and gets its name because of its use in Russian glass.
Glauconite is a mineral of this type, though it lacks a characteristic property, and the "windows" which allow weak forms of radiation to pass through Geiger counters are usually made of these minerals. "Bird's eye" patterns are exhibited by two of these minerals when placed under cross-polarized light. One type of these minerals is a lithium source, lepidolite, and another has a chromium-rich variant called fuchsite and gets its name because of its use in Russian glass. Containing such minerals as biotites and muscovites, for 10 points, identify these phyllosilicate minerals, many of which exhibit perfect basal cleavage.
Glauconite is a mineral of this type, though it lacks a characteristic property, and the "windows" which allow weak forms of radiation to pass through Geiger counters are usually made of these minerals.
{micas}