Mica

three slabs of mica - the one in the foreground is very thin, very clear, nearly invisible

mica flakes can leave a kind of dainty writing

Seen in the Beaney House of Art & Knowledge ... it made me curious about this mineral ...

Mica flakes are brittle but withstand high temperatures and pressures (I remember old heating stoves, eg in mountain cabins, having little mica windows in their doors, so you could see when wood needed to be added).

Mica is not one mineral but a group with about 30 members, the three most common being muscovite, biotite, and lepidolite. They are composed of sheets of silicate tetrahedrons (read more about the technicalities here).

The nearly perfect basal cleavage (ie, the way it flakes into sheets)  is the most prominent characteristic of mica; it is explained by the hexagonal sheet-like arrangement of its atoms.

The word "mica" is derived from the Latin word mica, meaning "a crumb", and probably influenced by micare, to glitter, says wikipedia.

The artist Ilana Halperin etched mica flakes as part of "The Library", shown at the National Museums of Scotland last year ("rocks are books"...). Her show, "Learning to Read Rocks", opens at Tobermory, Isle of Mull, on 29 May (till 26 July).

etched mica by Ilana Halperin (via)