Mica has been used for many purposes over time and even in my short lifetime I have seen it in toasters, light fittings and as windows in coal-fired heaters. But what is this amazing mineral?
Mica is a silicate mineral that falls into the phyllosilicate group. Phyllosilicates are minerals whose structure is made up of silicon and oxygen atoms that form sheets. Within the structure can sit other atoms including Aluminum (which replaces some silicon atoms), Potassium, Sodium, Calcium, Iron, Magnesium and a host of rarer elements. Each of the sheets are weakly bonded together and those bonds can be easily broken and so the mineral cleaves along the sheets. (See our post about cleavage).
The term Mica actually refers to a group of minerals with varying chemistry dependent on the amount of 'other' atoms that sit within the structure. Common micas are Muscovite (KAl2(AlSi3O10)(F,OH)2) - a silver-white mica and Biotite (K(Mg,Fe)3AlSi3O10(OH)2) a black mica. However, there is a huge range of micas with varying chemistry and therefore colors.
Micas can be found in all three types of rocks - sedimentary, igneous and metamorphic. Large specimens of sheet mica, used for commercial purposes or for collecting are almost always found in course grain igneous pegmatites. The largest documented single crystal of mica was found in the Lacey Mine, in Ontario, Canada and it measured 10 m by 4.3 m and was 4.3 m thick!
Sheet mica, once used as a form of heat resistant glass, has found its real use in electronics. It resists high temperatures and is a great insulator (and that's why it is used to hold and the heating wires in my toaster), but it also takes on electrostatic charges with heating up, and so it is used in capacitors and other electronic components.
Flake mica, often a by-product of the mining or other materials, is used in the creation of drywall (gypsum plaster sheeting) and as a major additive to paint. It is used in other building products, such as in asphalt roofing shingles and even as part of the lubricant used in well drilling.
Mica is also often used as a pigment in makeup and candles.
Mica is a very versatile and useful mineral. Not only that, it is a great mineral to have in your collection....and who does not enjoy just pulling those sheets apart! Therapeutic Mica. Maybe that's my next great idea.