Introducing a flaky mineral:
MICA
The name, mica, comes from the Latin verb "micare" to shine and noun "mica" meaning "grain" and mica crystals in a stream bed look just like shiny grains.
Mica is composed of:
Oxygen
Silicon
Hydrogen
Aluminum
and Potassium, Calcium, or Sodium
plus iron, magnesium or manganese.Appearance:
Mica crystals looks like thin sheets, like stacks of loose paper.
The sheets have a glassy sheen.
They are translucent and multicolored.Hardness: 2 to 2.5
A knife scratches mica easily.
How to recognize mica in a rock:
Mica seems to spot you. It twinkles and looks like the thinnest, tiniest sheet of gold or silver.
Its extraordinarily thin sheets split easily and flex.
Weathering:
Micas weather into clays.
They are not resistant and weather relatively quickly.Where you can find mica in Salt Lake County:
- As crystals in the igneous rocks of Little Cottonwood Canyon (granites) and igneous rocks of the Oquirrh Mountains
- In the fine sediments of Little Cottonwood Creek in Little Cottonwood Canyon.
- In many igneous or metamorphic tombstones of local cemeteries.
- In wood-stoves that have "windows" of isinglass (mica).
Other:
Mica isn't as abundant as quartz, feldspar, or calcite but it's distinctive enough and common enough in igneous and metamorphic rocks to deserve attention. If you only want to memorize three names... the most important ones are: quartz, feldspar, and calcite.