Strong heat and pressure inside the Earth can cause minerals in rocks to change. For example, when shale is changed to slate, the fine quartz crystals of the shale become broken, flattened, and reoriented. The clay particles of shale recrystallize to form tiny flakes of mica. This realignment of the bits of quartz and mica result in a rock that splits easily into fine, thin sheets with smooth surfaces. This property makes slate ideal for chalkboards, roofing tiles, and paving tiles.
Fossils are the remains or evidence of plants and animals that are found in rock.
Fossils provide a record of life that existed on Earth millions of years ago. Some fossils are the actual plant or animal remains that have been altered or mineralized. This process occurs when the original materials in an organism are replaced by minerals. Other fossils are impressions made in soft sediment by organisms, such as the tracks of animals left in mud. Most living things decay when they die.