Igneous rock

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Igneous rock

  1. 1. ROCKS
  2. 2. IGNEOUS
  3. 3. Igneous Sedimentary Metamorphic The Rock Cycle
  4. 4. Rocks- naturally occurring combinations of mineral • 1. Most contain at least 2 minerals. • 2. A few have only 1 • 3. Only 20 minerals are commonly found in rocks. • James Hutton- first to say that rocks formed from molten materials, not from minerals crystallized by water as previously thought • Molten- a solid object formed from liquid material
  5. 5. I. Igneous Rock • A. Formation of igneous rock – 1. crystallization- as magma cools below ground, the movement of ions in the liquid slows and the ions arrange into solid, more orderly patterns – 2. Rate of Cooling- • A. slow cooling deep in the earth forms very large crystals.
  6. 6. 1. Rocks formed in this way are coarse- grained and called intrusive 2. examples: gabbo, granite
  7. 7. b. Faster cooling nearer the surface forms very small crystals 1. Rocks formed in this way are fine-grained and called Extrusive 2. examples: basalt, andesite, rhyolite
  8. 8. C. Instant cooling would result in rocks made of unordered atoms and no definite crystal pattern. 1. These are referred to as glass. 2. examples: obsidian, pumice
  9. 9. • d. When crystallization occurs in areas with much water, unusually large crystals may form. – 1. These are called pegmatites. – 2. They often contain valuable minerals and gems like beryl and topaz.
  10. 10. 3. Composition of Magma • A. silicon, oxygen, aluminum, sodium, potassium, calcium, iron, and magnesium are the 8 most common mineral materials. • B. some materials called volatiles (water vapor, CO2) also volatiles- materials commonly found as a gas at surface level temperatures and pressures c. minerals in magma will crystallize at different rates and temperatures giving igneous rocks varied appearances
  11. 11. 4. Igneous textures • A. texture- describes overall appearance of the rock based on size and arrangement of the interlocking crystals • B. Texture can reveal details about the environment in which the rock formed.
  12. 12. • 1. Fine-grained textures (called aphanitic) are in igneous rocks formed near the surface – A. individual minerals cannot be identified so classification is by color-light, intermediate, dark – B. many can have elongated openings called vesicles through which gases have escaped – C. igneous rocks formed with this texture are called extrusive
  13. 13. • 2. coarse-grained textures (called phaneritic) are in rocks that form deep in the ground – A. individual minerals can easily be identified due to the large crystals – B. igneous rocks formed with this texture are called intrusive
  14. 14. • 3. Some igneous rocks begin to cool deep below surface, then get brought upward to finish cooling more quickly – A. they have some large crystals and some very small ones – B. these have porphritic textures, with the large crystals called phenocyrsts and small ones called groundmass
  15. 15. 4. Glassy textures • A. form when magma is thrown upward during eruptions which cool them instantly • B. example: obsidian- looks like a dark chunk of man made glass, used in Native American arrowheads pumice- very light –weight rocks that have many vesicles and can float on air or water
  16. 16. Floating pumice
  17. 17. • 5. pyroclastic textures- igneous rocks that have pieces of ash, or other molten blobs imbedded in them. Ex: tuff
  18. 18. B. Bowen’s Reactive Series • 1. Shows the exact order in which minerals form as magma cools (depends on depth and elements present)
  19. 19. Pg. 73
  20. 20. 2. Sequence descriptions • A. olivine and pyroxene form first, are rich in iron and magnesium, and are very dense • B. igneous rocks that contain these dense minerals are called mafic rocks and are usually black or dark green – 1. they form from magma ~ 900º C (1620º F) - 1200ºC (2160ºF) – 2. ex: basalt- makes up most of ocean bottom, gabbro-found on many Pacific Islands
  21. 21. • C. igneous rocks that contain low-density minerals are called felsic and are light colored. – 1. they form from magma about 800ºC (1440º F) and contain quartz and feldspar minerals – 2. ex: andesite, rhyolite, and the most common rock of all *granite*
  22. 22. Uses of Igneous Rock • 1. Carvings and inscriptions made in granite can withstand weathering –Ex. Vietnam Veteran’s Memorial wall in Washington, D.C.
  23. 23. • 2. Pumice is ground up and used as a scouring powder • 3. Some igneous rocks have valuable minerals like iron, copper, and uranium mixed in.

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