1. Chapter Three
ROCKS

2. Section 3-1 Classifying Rocks
When studying a rock sample, geologists observe the rock’s color and texture and determine its mineral composition.
Using color and texture, geologists can classify a rock according to its origin.
Texture is the look that results from the size, shape, and pattern of the rocks grains.

3. 3-1 Coarse-grained: the grains are large and easy to see.
Fined-grained: the grains are small and can been seen under a microscope or hand-lens.
Some rock’s grains results from the shape of the crystals that form the rock.
In other rocks, the grain shapes result from fragments of other rock.

4. Texture

5. Texture

6. 3-1 The three major groups of rock are:
Igneous: forms from the cooling of molten rock.
Sedimentary: forms when particles of other rocks of the remains of plants and animals are pressed and cemented together.
Metamorphic: forms when an existing rock is changed by heat, pressure, or chemical reactions.

7. 3-2 Igneous Rock
Igneous rock is any rock that forms from magma or lava. Most igneous rocks are made of mineral crystals. Igneous rocks are classified according to their origin, texture, and mineral composition.

8. Classification of Igneous Rock

9. Extrusive Rock
Extrusive rock: is igneous rock formed from lava that erupted onto Earth’s surface.
Basalt is the most common extrusive rock.

10. Samples of Extrusive Rock

11. 3-2
Intrusive rock: Igneous rock that formed when magma hardened beneath the Earth’s surface.
Granite is the most abundant intrusive rock.
The texture of an igneous rock depends on the size and shape of its mineral crystals.

12. Texture may be fine-grained, coarse-grained, porphyritic, or glassy.
Fined-grained: rapid cooling lava forms fined-grained.
Coarse-grained: slow cooling lava forms coarse-grained.
Porphyritic: large crystals scattered on top of small crystals. This occurs when magma cools in two stages, first slow, and then rapidly as magma moves near to the surface.

13. Samples of Intrusive Rock Granite

14. Samples of Intrusive Rock Gabbros

15. Samples of Intrusive Rock Diorite

16. 3-2 Lava low in silica forms dark-colored rocks, such as basalt.
Magma that is high in silica usually forms light colored rocks, such as granite.
Many igneous rocks are hard, dense, and durable. People use igneous rock for tools and building materials.

17. 3-3 – Sedimentary Rock
Sedimentary rocks form from particles deposited by water and wind. Sand, mud, and pebbles. Sediment is small, solid pieces of material that come from rocks or living things.
Erosion: running water or wind loosen and carry fragments of rock.
Deposition: the process by which sediment settles out of the water or wind.
Compaction: the process that presses sediments together.
Cementation: the process in which dissolved minerals crystallize and glue particles of sediment together.

18. 3-3 There are three major groups of sedimentary rocks:
Clastic rock: sedimentary rock that forms when rock fragments are squeezed together. Sandstone is a clastic rock formed from the compaction and cementation of sand.
Organic Rock: forms where the remains of plants and animals are deposited in thick layers. Coal is formed from the remains of swamp plants and limestone is formed from the hard shells of living things – seashells.
Chemical Rock: when minerals that are dissolved in a solution crystallize. Chemical rocks also form from mineral deposits left when seas or lakes evaporate.

19. Samples of Sedimentary Rock
Sandstone

20. Samples of Sedimentary Rock
Gypsum

21. Samples of Sedimentary Rock
Shale

22. 3-4 Rocks from Reefs
Coral animals are tiny relatives of jellyfish that live together in vast numbers. They build skeletons that grow together to form a structure called a coral reef.
Coral reefs only form in warm, shallow tropical waters.
When coral animals die, their skeletons remain, and new corals build on top of them.
There are three types of coral reefs: fringing reefs, barrier reefs, and atolls.
A coral reef is really organic limestone.

23. Fringing Reef

24. Barrier Reef

25. Atoll Reef

26. Coral Reefs

27. Coral Reefs

28. 3-5 Metamorphic Rock
Every metamorphic rock is a rock that has changed its form. Heat and pressure deep beneath Earth’s surface can change any rock into metamorphic rock. Metamorphic rock can form out of igneous, sedimentary, or other metamorphic rock.
Geologists classify metamorphic rocks by the arrangement of the grains that make up the rocks.
Metamorphic rocks that have their grains arranged in parallel layers or bands are said to be foliated – slate is the most common.
Metamorphic rocks that have grains arranged randomly. Marble and Quartz.

29. Metamorphic Rock Samples

30. Metamorphic Rock Samples
Marble

31. Metamorphic Rock Sample
Quartz

32. 3-6 Rock Cycle
Forces inside Earth and at the surface produce a rock cycle that builds, destroys, and changes the rocks in the crust.
The rock cycle is a series of processes on and beneath Earth’s surface that slowly change rocks from one kind to another.

33. The Rock Cycle

34. Rock Pictures - Lava