Here’s how to interpret the clues about the source of sand:

Shape
The shape of a grain can indicate how far it has traveled from its source. Generally, rounded grains have been transported longer distances than angular grains have.

Color/Composition
Color is usually an indicator of composition—the type of rock a grain came from. For example, if a sand grain is a volcanic mineral, a volcano is the likely source of the sand. Grains of obsidian (volcanic glass), olivine (an olive-colored volcanic mineral), and magnetite (a dark, magnetic mineral) all indicate a volcanic source of sand. Grains of quartz and feldspar indicate a granitic source.

Surface features
The presence of pits or holes on the surface of a grain suggests a volcanic source. Uniform ridges or holes sometimes reveal that a grain is part of a shell or a piece of coral, indicating a marine source for the sand.

  !   Click each image and interpret the clues about the source of each sample. Add the name of each sample and further details to your answers for question 1.