Value of Rock

1
Value of Rock

• Tools - arrowheads, spear points, knives
  scrapers from flint, chert, and obsidian rock
• Today special scalpels from obsidian
• Rocks help answer questions about history of the
  earth and solar system.
• Provides clues about life-forms that lived
  billions of years ago.

2
Rock Cycle

• Rock cycle-a process by which one rock type
  changes into another.
• Three main types
• igneous
• sedimentary
• metamorphic

3
Sedimentary Rock

• Sedimentary rock is rock that forms when
  sediments are compacted and cemented together.

4
Metamorphic Rock

• Metamorphic rock is rock that forms when the
  texture and composition of a preexisting rock is
  changed by heat or pressure deep underground.

5
Igneous Rock

• Igneous rock is rock that forms from the cooling
  of magma.
• When magma flows out onto the earths surface, it
  is called lava.

6
Rock Classification

• Two important criteria
• composition
• texture
• Composition of rock is what the rock is made of.
• Texture is determined by the size, shape, and
  position of the grains in the rock.

7
Texture (Cont.)

• Fine-grained texture are made entirely of small
  grains, such as silt or clay particles.
• Coarse-grained texture is made of large grains,
  such as pebbles.
• Medium-grained texture is between fine and coarse
  grained.