I don't understand how to find cleavage when looking into the light. How do you tell if there is cleavage this way?

-- Randy Rosenthal (rrosenth@oswego.edu), February 09, 2001

Answers

You won't find cleavage by looking into the light. That would hurt your eyes :-)

Hold the sample and turn it about (use that wrist action!) to see if there are bright flashes that result from light reflecting off flat, smooth cleavage surfaces. If so, the mineral probably has cleavage. Just remember that crystal faces can be very smooth and shiny, too. But a crystal face is not a breakage surface -- cleavage is a breakage surface. Some minerals like halite and galena tend to have cleavage parallel to crystal faces, but there are minerals that have cleavage at angles to crystal faces. Also, quartz is an example of a mineral that has no cleavage at all, but can come in very nice crystals.

Hope that explains things better. Cleavage is probably the most difficult of the physical properties to describe correctly.

-- Sharon Gabel (gabel@oswego.edu), February 09, 2001.