Shop Windows to the Universe

Check out the fun Earth science related bumper stickers in our online store! Express yourself!
Calcite crystals
Click on image for full size
Windows Original.

Try the calcite optical illusion!

You can use perfect calcite crystals to make an optical illusion called double refraction. Calcite has unique optical properties that split a ray of light into two beams that are bent at different angles because they travel at slightly different speeds. This splitting of light means that you see double when you look through a calcite crystal. It looks like there is two of everything!

Make a small drawing on a piece of paper, much smaller than your crystal of calcite. Place a transparent crystal of calcite on top of the drawing on the piece of paper. Spin the crystal slowly in a circle. In one position, your drawing will appear as a single image, but as you rotate the crystal, the drawing will gradually split into two images. Your drawing appears as a single image only when both light beams are traveling the same speed. This happens when light is traveling parallel to the primary axis of the crystal.

Last modified April 25, 2003 by Lisa Gardiner.

Shop Windows to the Universe Science Store!

The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

Windows to the Universe Community

News

Opportunities

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

Calcite

Calcite is typically found in the sedimentary rock called limestone. It can also be the cement that holds other sedimentary rocks, such as sandstone, together. Outside the sedimentary rock spectrum, calcite...more

Whatís 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 donít need to look at the elements with sophisticated chemical tests....more

Quartz

Quartz is the second most common mineral in Earthís 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 Earthís 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

Type of Minerals

So far, over 2000 minerals have been found, and every year new ones are discovered. This is a pretty overwhelming number of different types of minerals, however, you don't need to know them all to be...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