phlogopite: a brown form of mica consisting of hydrous silicate of potassium and magnesium and aluminum
mica: any of various minerals consisting of hydrous silicates of aluminum or potassium etc. that crystallize in forms that allow perfect cleavage into very thin leaves; used as dielectrics because of their resistance to electricity
ostracoderm: extinct fish-like jawless vertebrate having a heavily armored body; of the Paleozoic