mica: [18] Latin mīca meant ‘grain’, and its original use in English (perhaps influenced by the similar but unrelated Latin verb micāre ‘shine’) was to ‘small shiny particles or platelets’ in certain sorts of rock. The modern application to a group of related silicates, which contain such shiny plates, dates from the 1790s. [mica etymology, mica origin, 英语词源]