Journal9/14/15 1. How is the classification of rocks and minerals different from each other? 2. What are the differences between intrusive and extrusive igneous rocks? 3. What are the three steps in the formation of sedimentary rocks?

Only Surviving 9/11 Rescue Dog Pictured with handler at Ground Zero – WTC Sept Now 16 years old, Bretagne received treats and toys in NY to thank her for her service as a search and rescue dog.

Weathering

Key Questions What is mechanical weathering? What is chemical weathering? What factors affect the rate of weathering?

Mechanical Weathering Physical forces break rock into smaller pieces Rock’s mineral composition does not change Increases total surface area

Causes of Mechanical Weathering Frost wedging Unloading Abrasion Biological activity

Frost Wedging Water in rock cracks freezes and expands slowly breaking the rock apart Common in mountains and cold regions Talus - large piles of rock that have broken loose from cliffs

Unloading Release of pressure due to erosion Exfoliation – outer layers expand more and break loose Large dome shaped formations Common with granite

Abrasion Abrasive materials in water or wind wear down rock over time

Biological Activity Plants, animals & humans can cause mechanical weathering Burrowing, roots, foot traffic, deforestation

Chemical Weathering Transformation of rock into one or more new compounds

Water Most important agent of chemical weathering Dissolved compounds from the atmosphere and ground cause chemical reactions with minerals within the rock

Rate of Weathering Three factors: Amount of mechanical weathering Rock characteristics Climate

Rate of Weathering Factor 1 – Rate of mechanical weathering The more mechanical weathering the more surface area More surface area = faster rate of chemical weathering

Rate of Weathering Factor 2 - Rock characteristics Number of cracks/ pores More porous = faster weathering Chemical composition Do the minerals dissolve easily in water or react with other compounds? Which rock will weather more quickly? B A

Rate of Weathering Factor 3 – Climate Temperature & Moisture are the driving force behind weathering Higher rates of mechanical weathering in areas with four seasons Chemical weathering slowest in arid & polar regions & faster in regions that are warm with a lot of rain