Lozenge-shaped “fish” of this material are a common component of mylonitic rocks. Potassium or sodium characterizes the common type of this material contrasted with a calcium-containing brittle type. (-5[1])In a solid-solution series of this material, annite sits (-5[1])opposite the magnesium endmember (-5[1])phlogopite. Domains named for this material separate quartz and feldspar layers in (*) slate. A typical chemical formula for this material contains one atom of potassium, two to three of a Y element, four of silicon, (-5[2])ten oxygen, and two fluorine or OH. (-5[1])Books of this material are often found (10[1])in pegmatites. This material, which has perfect basal cleavage, (10[2])includes biotite (10[3]-5[1])and muscovite (10[2])types. (10[2]-5[1])For 10 points, name this group of silicate minerals known (10[1])for easily flaking (10[4])and having (10[1])a shimmering (10[2])appearance. (10[1]-5[1])■END■ (10[12]0[6])