http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
v.1. Introduction to rocks & minerals. - 25 minutes. - v.2. Sedimentary rocks. - 18 minutes. - v.3. Metamorphic rocks. - 21 minutes. - v.4. Igneous rocks. - 18 minutes. -