Mica is a mineral — a kind of stuff in rock — that splits easily into very thin, flat, almost see-through sheets, like glass you could peel. You see the little flakes shining in some stones. Because a thin sheet can take heat and does not let electricity pass easily, people have used it in electrical instruments, and older stoves sometimes had mica windows so you could look at the fire. Ground mica also goes into some make-up to make skin look a little sparkly. It is not a metal, though a fresh flake can look a little like silver, and it is not the same thing as plastic glitter. English borrowed the word from Latin mīca, which meant a grain or a crumb — a fitting picture, because the mineral comes away in little flakes. You say MY-kuh.