how does limestone and granite mechanically weather differently?
142267
I think there is some over-generalizing going on here. \n\nThe short answer: Granite is going to be more susceptible where its crystalline grain structure can be attacked by mechanical weathering. Limestone is going to be more susceptible where its softness is a disadvantage to mechanical weathering. For many types of mechanical weathering there is going to be little difference. \n\nHave you ever been to Yosemite? Half Dome, in the famous photographs by Ansel Adams is a perfect example of exfoliation of granite in sheets. This is a mechanical weathering process related to pressure release. Granite might be more susceptible to this (I am speculating) but only because it is often being unburied from much greater depths. Jointing in limestone is often related to pressure release. \n\nTo answer this question properly you need to consider the different types of mechanical weathering. I will compare the ones I can think of.\n1. Exfoliation caused by pressure release:  From my own field observations in areas where glacial unloading has occurred I would say that this affects both granite and limestone in a similar manner. Both will break off in sheets or blocks. \n\n2. Exfoliation is caused by temperature change: I have no quantitative proof but my opinion based on observation is that limestone is less susceptible to this because it is held together by cement and internal porosity probably has some ability to absorb differential expansion. Granite on the other hand is composed of crystalline grains that have different expansion rates and are likely to split apart. \n\n3. Freeze-thaw: Limestone does have bedding planes, and often has jointing as well, that is susceptible to this.  Some limestone has open porosity that also will be subject to some freeze expansion. Probably limestone is more vulnerable to this. Granite is going to be slightly susceptible to this only to the extent that water can penetrate it or to the extent it has been jointed or weakened by exfoliation. \n\n\n4.  Abrasion: Wind erosion affects both limestone and granite. Limestone is softer so windblown sand grains are more likely to erode the limestone. \n\n5. Salt-crystal growth: This is very common in coastal settings and sometimes in desert settings where moisture in the air is likely to contain some salts. Many of these salts will expand as the moisture that carried them evaporates. Heat will also cause them to expand.  I would say that granite is again more susceptible because of its crystalline grain structure. However, there is a special situation for limestone that few people who have never been in a cave have ever observed. Limestone often contains small deposits of anhydrite within the limestone. Anhydrite is unstable under surface pressures and tends to absorb water becoming gypsum. It expands as it does this and causes the limestone to break, often in sheets, but sometimes in blocks.  In many caves this is a primary cause of ceiling collapse and it can even result in stoping (raising the ceiling of the cave upward). \n\n6. Trees, plants: I doubt that there is any difference here. Some granite might provide more nutrients from chemical weathering to plants than limestone does, and so encourage its own destruction by plant roots, but both rocks are going to be susceptible. \n\n7. Tectonic and regional jointing: Tectonic events can cause fracturing in both types of rock. Limestone might be more flexible and be less susceptible to fracturing from mild folding. Regional jointing is related to pressure release and depends more on the burial and unroofing history than the type of rock. I don’t think either one is going to be more or less susceptible in most situations. Limestone often exhibits joints that can be traced for tens of miles that are related to regional stress regimes (both shear and extensional) and I believe that granite will produce similar joints.  You might be surprised to learn that the shear strength of granite and limestone are very similar
828414
We are dealing with an illusion caused by grain size and moisture content here.  In fact sand is quite hard because it is made up of individual rock and mineral grains.  Limestone and quartz are pretty hard materials.  If a sand is damp, or has very small rounded grains, it can feel soft to the hand however.\n\nClays on the other hand are soft because they are created by the chemical weathering of other minerals (such as pyroxene or feldspar) and the individual clay units are microscopic in size.  Clays usually contain a high proportion of water in their structure as well (it can be as high as 70%).\n\nWhen a geologist in the field can't make out the whether a rock is a siltstone (clastic) or clay (chemical) because the grain sizes are too small to see, a simple test is to break off a small fragment put it between ones teeth.  If its chewy and soft, its a clay.  If its hard and gritty, its a silt. \n(Warning - experts only folks.  Some rocks contain poisonous minerals so don't go around randomly tasting rocks.)
621837
neither granite nor obisdian are minerals they are two different types of igneous rocks. basically molten granite cools slow generating large crystals, obsidian cools very fast giving it a glassy look and making it nearly impossible to pick out individual crystals
488315
Carbonic acid is the one that usually affects limestone bedrock.\n\nCarbonic acid forms when decaying matter interacts with filtering water.\n\nAs it moves down through cracks in the bedrock, it slowly dissolves the limestone. Over time the cracks grow & enlarge eventually making miles of underground caves & caverns.\n\nThe type of topography associated w/ dissolution of limestone bedrock is called Karst Topography.\n\nKarst simply refers to that which you can see above ground like sinkholes (collapsed caverns/caves) & Karst lakes (sinkholes filled w/ water).
323011
depend on the type of rock. what material or materials is it made of, is it granite or what?
437376
Waiting for proper weather to ensure a solid set. If it's too dry or too humid, too hot or too cold, the concrete may not set properly and will need to be removed and repoured.
553240
because Quartz (SiO) is very stable and resistant. Acid igenous rocks contain lots of quartz and thats what continents are basically ade of. These weather to produce sandstones, a very common form of sedimentary rock
931995
limestone minerals buffer the acid rain.  The acid reacts with the calcite, etc. in limestone and changes it to more neutral or even slightly basic.  Our groundwater, therefore, tends to have a higher pH even though the pH of rainwater is low.
762090
With ribbons in the structure (where the pressure changed the rock) just like gneiss\nWith sheets in the structure (also caused by pressure) just like schiste\nWithout ribbons or sheets (where heat changed the rock) just like marble
211211
You need to think about this in terms of the question, that is what one of these processes involves movement of sediment.\n\nWeathering does involve movement of sediment, since weathering includes lots of processes that break down rocks into smaller particles or even dissolve rocks. Dissolution of limestone by carbonic acid in water is weathering that 'moves' rock. Freeze-thaw weathering of sandstone breaks the sandstone into smaller particles that are carried away by water, gravity, and wind. \n\nDeposition is the end result of the process of moving sediment, and may be the only one that does not answer your question, but because it is part of the process of 'moving' sediment it probably counts. \n\nErosion definitely moves sediment. Soil, sand, and rock are eroded by moving water and transported to new locations. \n\nAbrasion results in 'moving' sediment. Glaciers abrade underlying rock and grind it into small particles. Wind blows sand grains against rock and abrades it and reduces it to smaller particles. \n\nI think the only correct answer here is "all of the above.”
572852
There are three major ways that rocks are formed. The first of these is from heat ie- igneous rocks. They are the volcanic rocks, among which are obsidian, and granite. Both obsidian and granite contain the same minerals but their different appearances are caused by differences in the speed of their cooling. Obsidian cooled very rapidly and has a glassy texture.  Granite cooled very slowly and the separate minerals crystallized into larger crystal. The three major minerals of granite and obsidian are quartz, feldspar, and mica, each cool at a different rate.\n\n\nGranite is an Intrusive rock=\nIgneous rock that cools and solidifies beneath the Earth’s surface\n\nObsidian is an Extrusive rock=\nIgneous rock that cools and solidifies at or very near earths surface eg- in a lava flow
850784
Its asking what rock types (lithologies) would form topographical highs. in other words which rock type would weather away and which would stay longer. the ones that stay will be your topographical highs.
1119893
No it is not. Oceanic crust is composed primarily of basalt. Basalt is an extrusive igneous rock that cools quickly. Other types of rock commonly found on or beneath the unconsolidated sediments on the ocean floor are sedimentary rocks like sandstone, limestone, and shale. \n\nGranite is found in continental land masses. (Granite is NOT a metamorphic rock.) It is an intrusive igneous rock that must cool very slowly to form granite. \n\nHere is a good explanation with some illustrations:\nhttp://www.athro.com/earth_science/rocks.html
558851
Two reasons:\n\n1.)  Chemical reactions tend to increase with temperature; the same would be true for chemical weathering.\n\n2.)  Save for deserts, warm areas tend to be rainier, and a warm, wet climate makes for rapid weathering.
856161
By unit volume, probably dry cement is heavier. Why? Because rocks are heavier than water.
373520
Acidic rainfall dissolves soluble rock, such as limestone.\n\nThis article has some examples and pictures of Karst topography:  http://en.wikipedia.org/wiki/Karst
627781
Limestone becomes marble in metamorphosis.\nShale becomes schist.\nSandstone becomes granite.