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. In a solid-solution series of this material, annite sits opposite the magnesium endmember 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[1])ten oxygen, and two fluorine or OH. Books of this material are often found (10[1])in pegmatites. This material, which has perfect basal cleavage, (10[1])includes biotite (10[1])and muscovite types. (10[2])For 10 points, name this group of silicate minerals known for easily flaking (10[1])and having a shimmering (10[2])appearance. ■END■