Gemstones have value not only because they are beautiful, but also because there are rare.  So what exactly is a gemstone, and what make them so rare? 
Lee Groat is a Professor in the Department of Earth, Ocean, and Atmospheric Sciences at the University of British Columbia.   He studies the mineralogy of gemstones and also works in the field, having conducted surveys of parts of northern Canada looking for emeralds.
Go to geologybites.com for images of the gemstones discussed in the podcast and to learn more about Geology Bites.