Mica minerals! Biotite is on the left and muscovite is on the right.
Click on image for full size
Lisa Gardiner/Windows to the Universe

Mica Minerals

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!)

Last modified January 24, 2008 by Lisa Gardiner.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

What’s That Mineral?

Each type of mineral is made of a unique group of elements that are arranged in a unique pattern. However, to identify minerals you don’t need to look at the elements with sophisticated chemical tests....more

Granite Rocks

As granite is an intrusive igneous rock, a close look at a piece of granite will reveal that there are crystals of common silicate minerals within it such as quartz, plagioclase feldspar and orthoclase...more

Did Life First Develop in a Mica Sandwich at the Bottom of a Primordial Sea?

Earth's first life form may have developed between the layers of a chunk of mica sitting like a multilayered sandwich in primordial waters, according to a new hypothesis. The mica hypothesis, which was...more

Quartz

Quartz is the second most common mineral in Earth’s crust. It is a member of the quartz group, which includes less common minerals such as opal, crystobalite, and coesite. Silica (Si) and Oxygen (O) are...more

Mica Minerals

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...more

Feldspar

Feldspar is the most common mineral in the Earth’s crust, so you are very likely to find it in the rocks you collect! It is found it all of the three rock types, but is most common in intrusive igneous...more

Olivine

Olivine looks like little green crystals. It is typically found in some igneous and metamorphic rocks. Often the crystals are so small that you need to use your hand lens or magnifying glass to see them...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA