Classifying Rocks.
The way that Geologists classify a rock is if it is a sedimentary,metamorphic or igneous rock. An igneous rock is a rock that has been formed when magma or lava cools. A metamorphic rock is a rock that usually forms deep underground and forms when a rock that is already existing is changed by heat,pressure or chemical reactions. A sedimentary rock is a rock that forms when other rocks particles or plants and animals remains are pressed together.
Here is a website that will help you classify rocks: http://www.empr.gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/InformationCirculars/IC1987-05/Pages/classified.aspx