° -Where is the acid coming from? When CO2 reacts with water you form carbonic acid Much of the acid rain is in fact carbonic acid ° -Rain with acidic ph, which erodes the marble, but the granite doesn’t react as quickly. ° -Lesson, don’t get a marble tombstone, get one made out of granite. ° ° ° ° Chemical weathering of pyrite (rusting)(oxidization) ° -Iron sulfide mineral (fools gold) ° -Oxidizing it, adding water, which forms the material and sulfuric acid. ° -Net result: If you have rocks with pyrite in them, they will rust. ° -Old limestone buildings often gets rusted when there’s a small amount of pyrite (iron sulfide that oxidizes). ° ° Joints and Weathering ° -Joints: natural cracks that form in rocks due to removal of overburden or due to cooling) ° -Horizontal and vertical fractures, most rocks are jointed. Fine grained rocks: vertical and horizontal fractures will be much closer together. Courser grains, the fractures will be further apart. ° -Fractures assist physical weathering. ° -From a chemical perspective, if we have fractures, we have joints, we can dissolve along those fractures. ° -How to joints form?
1) If you cool lava, it will joint. When you turn a liquid into a solid, the liquid will occupy more space that the solid. o The reason: suppose lava flow occupies a certain volume. When it’s a solid, it wants to occupy less volume, but its physically laid out that way, so it will crack. (liquid water-solid is the opposite- it’s the exception). 2) Relieving pressure o Rocks buried deep in the earth’s crust endure enormous pressure due to the weight of overlying rock. o Over long periods of time, moving water, air, and ice at the earth’s surface grind away and remove overburden (erosion). o The result: rock formerly at depth rises closer to the surface, so the pressure squeezing this rock decreases. o The solid will be allowed to expand- t his causes the rock to change shape slightly, causing it to break. ° ° -The importance, joints help with physical and chemical weathering. ° ° ° Surface Area and Weathering ° -The greater the surface area, the more cracks, the faster the weathering. ° °
° ° ° Rounding effects of weathering ° -With chemical weathering, you’ll round the corners, the faces the most slowly. ° -Will turn a cube into a sphere. ° ° ° Transport and Sedimentation ° -The effect of transport ° -If we are close to the source of the sediment, we tend to get large particle, further away, fine grained. °
° ° ° Clastic Sediments ° -One major class of sedimentary rock (based on mode of origin) ° -Clast: broken piece ° -Clastic sediment is simply a rock that is made up of fragment. ° -In detail: ° ° ° -Angular: haven’t had time to be transported down river (with their edges broken off) ° -As we move them, they are changing shapes, simply because edges are being knocked off. (Because smaller and more rounded).
- Fall '09
- Sedimentary rocks, rocks