Mica

Micas are rock-forming minerals found worldwide. Muscovite and biotite are the most abundant and occur in granite, schist and gneiss; several micas were first described from Japan, including masutomilite, tobelite and kinoshitalite.

Mica is recognized by its one perfect cleavage, which lets it peel into thin, bendable, elastic sheets with a vitreous to pearly luster; the sheets also conduct heat and electricity poorly. Which mica a specimen is depends on its chemistry: for example, chromium-bearing green muscovite is called fuchsite, and lithium-rich pink to purple micas are called lepidolite. Biotite is a field name for dark micas rather than an independent species.

Mica was probably used in the mineralogical sense by 1706; the older word isinglass, known from at least 1535, was also applied to it. In Japan the old names kirara and kira for mica appear in the Wamyō Ruijushō dictionary (about 934), and mica was also used as a traditional medicine. In ukiyo-e woodblock prints, the kira-zuri technique applied mica powder (often replaced by clamshell powder) to backgrounds; it was especially popular in the 1790s on the large-head portraits by Kitagawa Utamaro and Tōshūsai Sharaku.