6.2 and 6.3 Flashcards
What are clastic sedimentary rocks?
Formed from the abundance of loose sediments found on Earth’s surface.
What are the three types of clastic sedimentary rocks?
Course-grained
Medium-grained
Fine-grained
What are coarse-grained clastics? What are the two types?
Sedimentary rocks consisting of gravel sized rock and mineral fragments.
1) Conglomerates- coarse-grained sedimentary rocks that have rounded fragments.
2) Breccias- coarse-grained sedimentary rocks that have angular fragments.
Both types form when gravel is transported by water and becomes abraded and rounded. The angular particles in Breccias indicate that particles did not have time to become round as they were transported only a short distance.
What are medium-grained clastics? When is sandstone formed? What are two important features of sandstone. Why is sandstone a valuable reservoir?
Sedimentary rocks that contain sand sized rock and mineral fragments. When these medium sized rocks are buried and lithified, sandstone is formed. Two important features of sandstone are its ripple marks and cross-bending which indicate the direction of current flow, and its high porosity which is the percent of open spaces between grains of rock. When pore spaces are connected, fluids can move through sandstone which make these layers valuable as reservoirs of oil, natural gas, and groundwater.
What are fine-grained clastics? What are two types? Why is the movement of groundwater and oil hindered?
These sedimentary rocks that consist of silt and mud are called siltstone and mudstone (shale). Siltstone is composed of silt-sized grains, whereas shale is composed of silt and clay sized particles. Shale breaks along thin layers and has low porosity which form barriers that hinder the movement of groundwater and oil.
What are chemical sedimentary rocks?
During chemical weathering, materials can be dissolved and carried into lakes and oceans and as water is evaporated from the lakes and oceans the dissolved minerals are left behind
How are rocks formed from evaporation? What are these layers called? What are the three most common types?
When the concentration of minerals in a dissolved body of water reaches saturation, crystal grains precipitate out of the solution and settle to the bottom. Layers of the chemical sedimentary rocks that form as a result are called evaporites. The three most common evaporate minerals are calcite, halite, and gypsum.
What are organic sedimentary rocks formed from?
The remains of once living things.
What is the most abundant organic sedimentary rock? What is it formed from primarily?
Limestone, primarily of calcite.
How is limestone formed?
Some organisms that live in oceans use the calcium carbonate dissolved in seawater to make their shells. When these organisms die, their shells settle to the bottom of the ocean and can form thick layers of carbonate sediment. During burial and lithification, calcium carbonate precipitates out of water, crystallize between the grains of carbonate sediment and form limestone.
What are the causes of metamorphism? What can regional metamorphism be? What is contact metamorphism? Why is hydrothermal metamorphism?
Different temperature and pressure combinations result in different types of metamorphism. Different types show different minerals and textures. Regional metamorphism can be low, intermediate, and high grade. This reflects the temperature and pressure. When molten rocks come into contact with solid rock, a local effect called contact metamorphism occurs. When very hot water reacts with rock and alters its chemistry and mineralogy hydrothermal metamorphism occurs. Hydrothermal fluids can dissolve some minerals, break down others, and deposit new ones.
What are the two textural groups of metamorphism?
Foliated and non-foliated
What conditions are minerals with a foliated texture formed under? What do they look like?
Formed under high pressure during metamorphism which causes flat or needle like crystals.
What are non-foliated minerals like?
Lack mineral grains and are very blocky. Composed mainly of minerals that form with blocky crystal shape.
What are porphyroblasts?
Under certain conditions, new metamorphic minerals can grow quite large while the surrounding minerals remain small. The large crystals which can range in size from a few millimetres to a few centimetres are called porphyroblasts.
