Why doesnt quartzite weather as quickly as sandstone

Common intrusive igneous rocks are: granite, diorite, gabbro, and peridotite. The La Sal Mountains were formed by widespread igneous activity that began about 40 million years ago. Caldera explosions erupted thousands of cubic miles of volcanic rocks from several locations.

Volcanoes spewed ash and lava. For 20 million years these extrusive volcanic rocks smoothed the landscape, filling depressions with accumulations of ash, flows, and debris literally miles thick.

These mostly pastel-colored extrusive rocks still blanket much of the high areas of central and southwestern Utah. Not all of the molten rising igneous material erupted as volcanic rocks; some material, along with its mineral-bearing fluids, congealed in the earth's crust. Several of these intruded masses having been exposed by erosion or encountered out by exploration drilling became great mining districts, such as at Alta, Brighton, Bingham, Park City, and Cedar City.

In the Colorado Plateau, bodies of intrusive rocks domed the overlying sedimentary rocks to form the Abajo and Henry Mountains as well as the La Sal Mountains. NOTE: This paragraph on laccoliths borrowed from here. Rocks which have undergone these sorts of changes are called metamorphic rocks. Agents of Matamorphosis. The three primary agents which metamorphose rock are temperature, pressure, and fluids.

High temperatures can change rock by changing the structure of the minerals which make up the rocks; changing the structure of the minerals changes them into new minerals remember the definition of a mineral. This increase in temperature with increase in depth is called the geotherm. Intrusions Another source of high temperatures inside the Earth is magma intruding cooler rock.

These temperature increases are localized near the intrusion, but also metamorphose rock this is called contact metamorphism. Pressure or more properly, stress can also change rock. There are two main kinds I want you to know about: Confining Pressure Pressure due to the weight of overlying rock. This kind of pressure is roughly the same in all directions this is like water pressure when scuba diving , and is the kind which compacts rock during diagenesis.

Confining pressure changes rock by compaction and by changing the crystal structure of minerals from relatively open forms to more densely-packed forms. One mineral which does this is olivine, which changes from olivine isolated silica tetrahedra to spinel a much more tightly-bonded structure to perovskite a still more highly compressed structure.

This kind of pressure is usually due to tectonic forces. It changes rocks by changing the structure of minerals and by changing the orientation of mineral grains, particularly platy minerals like mica or clay. Fluids which metamorphose rock are not pore fluids remaining from when sedimentary rocks were deposited. Instead, they come from two main sources: hydrothermal fluids from magmatic intrusions and dehydration of minerals, like clay, which contain water in their structures hydrous minerals.

Whatever the source, fluids contain ions dissolved from other rock or from their original source. As fluids percolate through rocks, they can exchange ions with the existing minerals and thus change the chemical makeup of those minerals. The other way fluids change minerals is by hydrating minerals which previously did not contain water.

Either way, fluids change the chemical makeup of minerals, turning them into new minerals, which changes the rocks which were made of the previous minerals. This process of change by fluids is called metasomatism. Types of Rock Metamorphism. Some kinds of metamorphism: Burial Bury rocks deeply enough and they will warm up and change.

This form of metamorphism is found anywhere where sediments and rocks are buried deeply, and should strike you as being pretty similar to diagenesis, which we discussed last time. The line between diagenesis and burial metamorphism is fuzzy.

Regional Caused by widespread moderate-to-high temperatures and pressures, as opposed to localized changes along faults or near magmatic intrusions. You find this type of metamorphism in mountain building regions and near subduction zone volcanism. Contact Caused by high temperatures near magmatic intrusions. Found in volcanic regions subduction zones, hot spots and mountain building zones. Cataclastic Caused by grinding along fault zones.

Found along major faults like the San Andreas Fault in California , in mountain building zones, and in deformation regions associated with subduction zones. Hydrothermal Caused by hot fluids percolating through rocks. Found anywhere where hot fluids can percolate through rocks, notably along mid-ocean ridges.

Metamorphic Rocks and Rock Textures. Three major texture and rock types for metamorphic rocks that you need to know: Foliated Rocks Characterized by parallel planes formed through directed pressure and preferred growth orientations of certain platy minerals. Two common kinds are schist and gneiss, which have been used in a great many really bad geological puns. Non-foliated Rocks Don't have those planes, usually because they are made of mineral grains which are cubic or spherical, and therefore have no preferred orientation.

Two common examples are marble and amphibolites. Deformational Caused by cataclastic metamorphism. The most common rock of this kind is called a mylonite; there is a big mylonite belt in the mountains south of Palm Springs, CA.

Metamorphic Grade. Geologists who study metamorphic rocks have come up with the concept of metamorphic grade to describe how 'metamorphosed' a rock is.

More specific distinctions can be made through lab experiments in which various kinds of rocks are squeezed and heated up and the changes observed. Through this kind of work, geologists have found a set of index minerals , which are common minerals which form under particular combinations of pressure and temperature. Armed with knowledge from these experiments, field geologists can go out and make maps of mineral location to determine how metamorphism is distributed over large regions of rocks.

Metamorphic Facies. Keep that in mind: you get different minerals from different rocks under the same conditions and you get different minerals from the same rocks under different conditions. Geologists have formalized these statements into a system of classifications for rocks by pressure and temperature conditions, so that a given combination of pressure and temperature will give a specific class of rocks.

These classifications are called metamorphic facies. This is vital information for figuring out past tectonic conditions in the region, since certain facies form in certain plate tectonic environments. For example, blueschists form under low temperatures and moderate-to-high pressures, which indicates that the material which metamorphosed was shoved down into the Earth so quickly it didn't have much time to warm up.

What kind of plate tectonic environment displays these features? Subduction zones! Once material is weathered from rocks, it is transported away and later deposited somewhere else, and eventually is turned into new rocks. Such rocks are called sedimentary rocks , and they're the subject of this lecture. What are sediments? What is a sedimentary rock? Sediments are loose particles of former rocks.

Metamorphic rocks are almost always harder than sedimentary rocks. They are generally as hard and sometimes harder than igneous rocks. They form the roots of many mountain chains and are exposed to the surface after the softer outer layers of rocks are eroded away.

Many metamorphic rocks are found in mountainous regions today and are a good indicator that ancient mountains were present in areas that are now low hill or even flat plains. Metamorphic rocks are divided into two categories- Foliates and Non-foliates. Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage. Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock.

Slate, as an example, will split into thin sheets. Foliate comes from the Latin word that means sheets, as in the sheets of paper in a book.

Silt and clay can become deposited and compressed into the sedimentary rock shale. The layers of shale can become buried deeper and deeper by the process of deposition. Deposition is the laying down of rock forming material by any natural agent wind, water, glaciers over time.

Because these layers are buried, temperatures and pressures become greater and greater until the shale is changed into slate. Slate is a fine-grained metamorphic rock with perfect cleavage that allows it to split into thin sheets. Slate usually has a light to dark brown streak. Slate is produced by low grade metamorphism, which is caused by relatively low temperatures and pressures. Slate has been used by man in a variety of ways over the years. One use for slate was in the making of headstones or grave markers.

Slate is not very hard and can be carved easily. The problem with slate though is its perfect cleavage. The slate headstones would crack and split along these cleavage planes as water would seep into the cracks and freeze which would lead to expansion.

This freeze-thaw, freeze-thaw over time would split the headstone. Today headstones are made of a variety of rocks, with granite and marble being two of the most widely used rocks. Slate was also used for chalk boards. The black color was good as a background and the rock cleaned easily with water. Today it is not very advantageous to use this rock because of its weight and the splitting and cracking over time.

Schist is a medium grade metamorphic rock. This means that it has been subjected to more heat and pressure than slate, which is a low grade metamorphic rock. As you can see in the photo above schist is a more coarse grained rock. The individual grains of minerals can be seen by the naked eye.

Many of the original minerals have been altered into flakes. Because it has been squeezed harder than slate it is often found folded and crumpled. Schists are usually named by the main minerals that they are formed from. Bitotite mica schist, hornblende schist, garnet mica schist, and talc schist are some examples of this.

Gneiss is a high grade metamorphic rock. This means that gneiss has been subjected to more heat and pressure than schist. Below the surface, heat and pressure eventually transform igneous rock into metamorphic rock.

Above the surface, wind and water eventually weather away the igneous rock. The particles, called sediment, are carried away to be deposited in layers elsewhere, eventually becoming sedimentary rock.

As layer upon layer of sediment is deposited, water is squeezed out from between the particles and minerals and pressure cements the particles together, changing them into sedimentary rock.

Sandstone, in particular, is a sedimentary rock cemented together by calcite, clay or silica. Sedimentary rock becomes heated, either from pressure, friction, or radioactive decay.

As it bakes, it undergoes a metamorphosis, forming crystals, and eventually becomes metamorphic rock. Different combinations of heat and pressure on sedimentary rock form different types of metamorphic rock.

Quartzite, in particular, can be formed by either high temperature and high pressure or high temperature and low pressure. After this point, the rocks begin to melt, again forming magma beneath the surface of the Earth to begin the process all over again. When the sedimentary rock sandstone is cemented together by the mineral silica, it is known as quartz sandstone.