Correct Response: D. Muscovite mica and biotite mica are most easily identified by their perfect cleavage in one direction. They are both phyllosilicate minerals (also called sheet silicates) that form in thin layers. The specific gravity of these two related minerals (A) are similar, but specific gravity is not, in itself, a characteristic that can be used to identify the two minerals. Unlike carbonate minerals, these mica minerals cannot be identified by their reactivity to acids (B) and, unlike amorphous or fine-grained rocks such obsidian and chert, muscovite and biotite mica do not exhibit conchoidal fracturing when broken (C).
