Gneiss ( /ˈnaɪs/) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.
Shale is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces. The specimen shown above is about two inches (five centimeters) across.
Pumice is a light-colored vesicular igneous rock. It forms through very rapid solidification of a melt. The vesicular texture is a result of gas trapped in the melt at the time of solidification. The specimen shown above is about two inches (five centimeters) across.
Types of peridotite - Peridotite is a generic name for a number of different rock types. All of them are rich in olivine and mafic minerals. They are usually green in color and have a high specific gravity for a nonmetallic material. Shown above are specimens of lherzolite, harzburgite, dunite, and wehrlite. Image by USGS.