Topic 1 Geology of Earth Flashcards
Four Qualities of a Mineral
“Crystalline Solid
Minerals are crystalline solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. The pattern of atoms in different samples of the same mineral is the same. Is glass a mineral? Without a crystalline structure, even natural glass is not a mineral.
- Inorganic Substances
Organic substances are the carbon-based compounds made by living creatures and include proteins, carbohydrates, and oils. Inorganic substances have a structure that is not characteristic of living bodies. Coal is made of plant and animal remains. Is it a mineral? Coal is a classified as a sedimentary rock but is not a mineral. - Natural Processes
Minerals are made by natural processes, those that occur in or on Earth. A diamond created deep in Earth’s crust is a mineral. Is a diamond created in a laboratory by placing carbon under high pressures a mineral? No. - Chemical Composition
Nearly all (98.5%) of Earth’s crust is made up of only eight elements – oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium – and these are the elements that make up most minerals.”
Physical Characteristics of a Mineral
“hardness (mineral’s ability to scratch or be scratched by another mineral)
density (how much matter in a certain amount of space)
luster (sparkly or dull)
streak, which is the color of the mineral’s powder that is left behind when the mineral is scratched across an unglazed porcelain surface.”
Chemical Formulas
“All minerals have a specific chemical composition. The mineral silver is made up of only silver (Ag) atoms and diamond is made only of carbon (C) atoms, but most minerals are made up of chemical compounds. Each mineral has its own chemical formula. Halite, pictured in green and purple, is NaCl (sodium chloride). Quartz is always made of two oxygen atoms bonded to a silicon atom, SiO2. If a mineral contains any other elements in its crystal structure, it’s not quartz.”
What is a rock made of?
“A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples below the same rock type? Do they have the same minerals? The same texture”
Differences in how rocks are formed
“Magma is melted rock inside Earth, a molten mixture of substances that can be hotter than 1,000oC. Magma cools slowly inside Earth, which gives mineral crystals time to grow large enough to be seen clearly.
When magma erupts onto Earth’s surface, it is called lava. Lava cools much more rapidly than magma when it is below the surface. In a cooling lava, mineral crystals do not have time to form and are very small. The chemical composition will be the same as if the magma cooled slowly.
Existing rocks may be heated enough so that the molecules are released from their structure and can move around. The molecules may match up with different molecules to form new minerals as the rock cools. This occurs during metamorphism”
Intrusive igneous rocks
“Igneous rocks are called intrusive when they cool and solidify beneath the surface. Intrusive rocks form plutons and so are also called plutonic. A pluton is an igneous intrusive rock body that has cooled in the crust. When magma cools within the Earth, the cooling proceeds slowly. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Granite is the most common intrusive igneous rock.”
Extrusive igneous rock
“Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks.
Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals.
Cooling rate and gas content create other textures. Lavas that cool extremely rapidly may have a glassy texture. Those with many holes from gas bubbles have a porous texture.”
Sedimentary rocks
“Sedimentary rocks form by the compaction and cementing together of sediments, broken pieces of rock-like gravel, sand, silt, or clay. Those sediments can be formed from the weathering and erosion of preexisting rocks. Sedimentary rocks also include chemical precipitates, the solid materials left behind after a liquid evaporates.”
Metamorphic rocks
“Metamorphic rocks form when the minerals in an existing rock are changed by heat and/or pressure within the Earth. In the large outcrop of metamorphic rocks (top right), the rocks’ platy appearance is a result of the process metamorphism. The heat and/or pressure that existing rocks undergo causes them to change physically and/or chemically so that they become a new rock. Metamorphic rocks may change so much that they may not resemble the original rock.”
Metamorphism
“Any type of rock – igneous, sedimentary, or metamorphic - can become a metamorphic rock. All that is needed is enough heat and/or pressure to alter the existing rock’s physical or chemical makeup without melting the rock entirely. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange and form new minerals. Ions may move between minerals to create minerals of different chemical composition.”
The rock cycle
“the three main rock types – igneous, sedimentary, and metamorphic - are shown. Arrows connecting the three rock types show the processes that change one rock type into another. The cycle has no beginning and no end. Rocks deep within the Earth are right now becoming other types of rocks. Rocks at the surface are lying in place before they are next exposed to a process that will change them.”
Stenos laws
Original Horizontality- sediments are deposited into flat layers
Lateral Continuity- sediments deposited in continuous sheets that span the body of water
Superposition- sediments are deposited on top of one another. The youngest layers are found on the top, and the oldest on the bottom.
Hutton’s principle of cross cutting relationships
“The Colorado River cuts through all the layers of rock to form the canyon. Based on the principle of cross-cutting relationships, the river must be younger than all of the rock layers that it cuts through.”
Forms of absolute dating
Tree rings
Drilling thick sheets of ice
Radioactive Decay
Looking at various forms of sea sediment
Hutton’s uniformitarianism and Unconformity
“Hutton formulated uniformitarianism: The present is the key to the past. According to uniformitarianism, the same processes that operate on Earth today operated in the past as well. Why is an acceptance of this principle absolutely essential for us to be able to decipher Earth history?
Hutton questioned the age of the Earth when he looked at rock sequences. On his travels, he discovered places where sedimentary rock beds lie on an eroded surface. At this gap in rock layers, or unconformity, some rocks were eroded away.
