GEOL 108 - Crises of a Planet Lab 5 - Rocks, Weathering, and Minerals

Oct. 2 - 5, 2012

Department of Earth Sciences

Department of Earth Sciences REVIEW | 2

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Solid  Bedrock  

Unconsolidated  sediments  

 A  large  earthquake  occurs  with  the  epicenter  at  point  C.    Is  there  likely  to  be  more  damage  at  point  A  or  at  point  B,  and  why?    

Bonus:  Name  these  3  cartoon  dogs  (1  pt).  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 3

LAB 5 - ROCKS, WEATHERING, AND MINERALS •  Identify minerals

•  Compare clay properties

•  Relate weathering of rocks to clay formation

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 4

WHAT IS A MINERAL? •  Definition of a Mineral:

1.  naturally occurring 2.  inorganic 3.  solid 4.  characteristic crystalline structure 5.  definite chemical composition

steel plastic sugar table salt mercury ice coal

basalt obsidian mica gold paper chalk coral

no, #1 no, #1 no, #1,2 YES! no, #3 YES! no, #2

no, #5 no, #4 YES! YES! no, #1,2 no, #2 no, #2

Source:  www.sci.uidaho.edu/geol111/Geology%20101/minerals_II_jh.ppt  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 5

LUSTER •  Metallic  •  Non-­‐metallic  − Glassy  (vitreous)  − Waxy  − Silky  − Greasy  − Earthy  (dull  and  powdery)  

− Pearly  

Shiny  ≠  metallic!  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 6

COLOR

•  In  general,  color  is  not  a  diagnosPc  property  −  ImpuriPes  in  the  crystal  can  change  the  color  −  Color  is  less  variable  for  minerals  with  metallic  luster  

hRp://nature.berkeley.edu/classes/eps2//wisc/jpeg/l15s32.jpeg  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 7

STREAK

•  Streak  is  the  color  of  a  mineral’s  powder  •  A mineral’s streak is the same for all specimens

regardless of apparent color.

Example:  Metallic  and  earthy  hemaPte  (Fe2O3)  both  have  red-­‐brown  streaks.  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 8

CLEAVAGE •  A  specific  type  of  breakage  •  Occurs  because  bonds  between  atoms  are  weaker  in  some  direcPons.    

•  There  may  be  up  to  6,  but  usually  1-­‐3  •  Angles  between  cleavage  direcPons    

1  direcPon  2  direcPons  3  direcPons  (90°)                    3  direcPons  (not  90°)  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 9

CLEAVAGE •  One  direcPon  of  cleavage  

Example:  Mica  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 10

CLEAVAGE •  Two  direcPons  of  cleavage  

feldspar

hornblende

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 11

FRACTURE •  No  planes  of  weakness    leads  to  irregular  or    conchoidal  fracture  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 12

CRYSTAL HABIT •  A  crystal’s  habit  is  the  shape  it  takes  when  it  grows  unimpeded  by  other  grains  (somewhat  rare).  

•  Commonly  confused            with  cleavage.  

Two  intergrown  Staurolite  crystals  “St.  Andrew’s  Cross”  twinning  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 13

HARDNESS •  What  can  a  mineral  scratch  and  what  is  it  scratched  by?  It  will  only  be  scratched  by  harder  material.  

•  Please  don’t  test  samples  on  each  other!  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 14

OTHER PROPERTIES

•  Specific  Gravity  (density  compared  to  water)  •  MagnePsm    •  ReacPon  to  acid  (Carbonate  minerals  –CO3)  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 15

THE ROCK CYCLE  

Clays  

Department of Earth Sciences ROCKS, WEATHERING, MINERALS | 16

CLAYS Group  of  minerals,  commonly  found  in  sedimentary  rocks   montmorillonite kaolinite illite  

(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·∙nH2O    Al2O3·∙2SiO2·∙2H2O    (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)]