Mica Minerals



Mica minerals! Biotite is on the left and muscovite is on the right.
Click on image for full size version (276K JPG)
Windows to the Universe Image

Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage. These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book. Colonial Americans used the “pages” of large mica crystals as glass for windows.

The characteristics of the two most common types of mica are listed below. Notice how they are very similar in all ways except for their color? That is how you can tell them apart!

Biotite

  • Shape: Monoclinic . Forms flat plates.
  • Luster: Pearly, metallic
  • Color: Dark brown, dark green or black
  • Streak: White
  • Hardness: 2.5-3 on Mohs Hardness Scale
  • Cleavage: Yes, one plane of cleavage
  • Fracture: The mineral is rather flexible and so it doesn’t fracture very easily. In fact you can bend it very far before it breaks.

Muscovite

  • Shape: Monoclinic. Forms flat plates.
  • Luster: Pearly, metallic
  • Color: Colorless or lightly tinted
  • Streak: White
  • Hardness: 2-3 on Mohs Hardness Scale
  • Cleavage: Yes, one plane of cleavage
  • Fracture: This mineral is also flexible and doesn’t fracture very easily.
(...and learn what shape, luster, color, streak, hardness, cleavage and fracture are all about!)

Did Life First Form in a Mica Sandwich at the Bottom of an Ancient Sea?

Find out how to identify minerals(...and learn what shape, luster, color, streak, hardness, cleavage and fracture are all about!)

Meet some other silicate minerals!


Mica Minerals



Mica minerals! Biotite is on the left and muscovite is on the right.
Click on image for full size version (276K JPG)
Windows to the Universe Image

Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage. These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book. Colonial Americans used the “pages” of large mica crystals as glass for windows.

The characteristics of the two most common types of mica are listed below. Notice how they are very similar in all ways except for their color? That is how you can tell them apart!

Biotite

  • Shape: Monoclinic . Forms flat plates.
  • Luster: Pearly, metallic
  • Color: Dark brown, dark green or black
  • Streak: White
  • Hardness: 2.5-3 on Mohs Hardness Scale
  • Cleavage: Yes, one plane of cleavage
  • Fracture: The mineral is rather flexible and so it doesn’t fracture very easily. In fact you can bend it very far before it breaks.

Muscovite

  • Shape: Monoclinic. Forms flat plates.
  • Luster: Pearly, metallic
  • Color: Colorless or lightly tinted
  • Streak: White
  • Hardness: 2-3 on Mohs Hardness Scale
  • Cleavage: Yes, one plane of cleavage
  • Fracture: This mineral is also flexible and doesn’t fracture very easily.

Did Life First Form in a Mica Sandwich at the Bottom of an Ancient Sea?

Find out how to identify minerals(...and learn what shape, luster, color, streak, hardness, cleavage and fracture are all about!)

Meet some other silicate minerals!


Mica Minerals



Two colors of mica!
Click on image for full size version (276K JPG)
Windows to the Universe Image

Mica minerals make some rocks sparkle!

Look for them in your igneous and metamorphic rocks. Do they make your rocks sparkle?

They break into flat plates because they have cleavage.


Did Life First Form in a Mica Sandwich at the Bottom of an Ancient Sea?

Find out how to identify minerals!

Meet some other silicate minerals!



Last modified January 24, 2008 by Lisa Gardiner.
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