1. Rocks &
the Rock Cycle

2. The underlying principle for understanding all things geological is:
Minerals and rocks are stable only under the conditions at which they form.
Change the conditions and the rocks
will change to adapt to the new conditions.

3. Rock - an aggregate of one or more minerals
Let’s start at the very beginning…
Mineral (review) – Naturally occurring inorganic solid materials with definable chemical compositions and an orderly arrangement of atoms within a lattice.
Rock - an aggregate of one or more minerals

4. Three main rock types ~ Igneous ~ Sedimentary ~ Metamorphic
Let’s start at the very beginning…
Three main rock types
~ Igneous
~ Sedimentary
~ Metamorphic

5. Igneous Part of the Rock Cycle
Pyroclastic material
Lava
Igneous Part of the Rock Cycle
Igneous part of rock cycle is constructive force, creating new crust and or rocks.

6. Magma is molten material below the surface
Igneous Rocks
All igneous rocks
cool and crystallize from magma (inside)
or solidify from lava (outside)
or consolidate from pyroclastic materials (outside)
Magma is molten material below the surface
Lava is molten material on the surface
Pyroclastic materials
particles such as volcanic ash, volcanic bombs, tephra, etc.

7. Classification of Igneous Rocks
Igneous rocks are classified by composition and texture.
Composition = what it’s made of
Texture = how it’s put together.

8. Composition
Composition – These categories are based on silica content.
“Granitic” igneous rocks - (AKA - Felsic igneous rocks) Light-colored igneous rocks made from felsic (light-colored) minerals such as quartz, micas, and feldspars.
“Basaltic” igneous rocks - (AKA - Mafic igneous rocks) Dark-colored igneous rocks made of mostly mafic minerals such as olivines, pyroxenes, amphiboles, and Calcium-rich plagioclase.
The terms the book uses for these rocks (Granitic and Basaltic) are a poor choice, as we will see….

9. Texture
Texture - the size, shape and arrangement of crystals, grains and other components of the rock. Texture is controlled by the rate of cooling and crystallization.
Extrusive (“outside earth”) – cools quickly to instantaneously. Crystals do not have time to grow to visible size.
formed at the surface from lava or pyroclastic materials
Example: Basalt, Pumice
Intrusive (“inside earth”) – cools slowly over loooooong periods of time, allowing crystal growth to occur. Produces crystals visible to the naked eye.
formed below the surface
Example: Granite
So why are the book terms of “Granitic” and “Basaltic” not good terms to use?

10. Differences in Texture
Extrusive texture
Rapid cooling
Intrusive texture
Slow cooling
Vs.

11. Extremely fast cooling
Extrusive Textures
Glassy texture
Extremely fast cooling
Vesicular texture
Created by escaping
gasses trapped in
cooling lava

12. Spear tips made from rainbow obsidian
The iridescent, rainbow-like sheen of rainbow obsidian is caused by inclusions of magnetite nanoparticles.
Say what?
Tiny pieces of the mineral magnetite are trapped in the molten rhyolite magma when it cools very fast.
Spear tips made from rainbow obsidian

13. Common Intrusive Igneous Rocks
Granite
Slow cooling magma allows crystals to grow to visible size
Gabbro
Felsic
Mafic
Composition

14. Common Extrusive Igneous Rocks
Basalt
Fast cooling, typically in the form of lava, prevents crystals from growing to a visible size
Rhyolite
Mafic
Felsic
Composition

15. Extrusive texture (cooled quickly)
Rhyolite
Extrusive texture (cooled quickly)
Felsic composition (light in color)
When rhyolite lava cools extremely quickly, it forms obsidian.

16. Slow cooling allows the crystals time to grow to a visible size
Granite
Intrusive texture
(slow cooling)
Felsic composition
(light in color)
Slow cooling allows the crystals time to grow to a visible size

17. Holes are produced by gas escaping rapidly as it cools.
Scoria
Vesicular texture
(fast cooling)
Holes are produced by gas
escaping rapidly as it cools.

18. (cooled extremely fast)
Glassy texture
(cooled extremely fast)
Obsidian

19. Cooling Rate = ?
Composition = ?
Texture = ?

20. Cooling Rate = ?
Composition = ?
Texture = ?

21. Cooling Rate = ?
Composition = ?
Texture = ?

22. Cooling Rate = ?
Composition = ?
Texture = ?

23. Cooling Rate = ?
Composition = ?
Texture = ?

24. Cooling Rate = ?
Composition = ?
Texture = ?

25. Cooling Rate = ?
Composition = ?
Texture = ?

26. Famous Igneous Rocks!!

27. Igneous rocks - Review Igneous rocks – form from cooled molten rock
Magma
Lava
Textures – 2 types, know how each type forms
Extrusive
Intrusive
Composition – 2 types
Felsic
Mafic

28. Sedimentary
Rocks

29. Sediment The Sedimentary Cycle
Sediment is created through the process of weathering…
Sediment
Loose particulate material or residue (clay, sand, gravel, etc.) from a specific source (biochemical, chemical, detrital).
Weathering
Transport
Uplift
Deposition
Lithification
The
Sedimentary
Cycle

32. Weathering = Making sediments
Two types of weathering:
Chemical – decomposing or
dissolving of Earth material
Physical – cracking, scratching, abrasion,
or other physical breaking up of Earth material
(clasts, rock fragments, mineral grains from inorganic sources; peat, shell gravel from organic sources)
Weathering
Transport
Uplift
Deposition
Lithification
The
Sedimentary
Cycle

33. Chemical Weathering

34. Physical Weathering

35. Weathering

36. Transport
Moving sediments from where they were formed to where they are deposited
Transported by
wind, water, and/or ice

37. Transport by Wind

38. Transport by Water

39. Transport by Ice

40. Deposition
Sediments are ‘deposited’ somewhere like a lake, river, or other area where the wind, water, or ice will not move them any further.

41. Alluvial Fans

42. Braided Stream  

43. Deltas

44. Meandering Rivers  

45. Lithification = “Turned to stone”
Once deposited, sediments turn to sedimentary rocks by one or more of these processes:
Compaction
Cementation
Precipitation / Evaporation

47. METAMORPHIC ROCKS
“Change of form”

48. Metamorphic
Rocks

49. The rock that is changing does not melt during metamorphosis
Metamorphic rocks are formed when heat and pressure changes another rock
The rock that is changing does not melt during metamorphosis
What would we call it if it did melt?

50. Metamorphic rocks can be formed from:
What can be changed?
Metamorphic rocks can be formed from:
 Igneous rocks
 Sedimentary rocks
 Other metamorphic rocks

51. Metamorphic Rock Classification
Metamorphic rocks are broken out into two main groups, foliated and non-foliated.
Foliated – Have bands of different colored minerals
Non-foliated – No layering or banding present

53. Where on Earth?

54. The Rock Cycle – A Different View