The Rock Cycle

What are the three major types of rocks?

igneous, metamorphic, and sedimentary

any of these three rocks can be converted into the other via the rock cycle

Igneous Rocks

burning molten rock

when it is below the earths surface, it is called magma, when it erupts, it is called lava

once it hits the earths surface, it cools very quickly therefore the rock has many imperfections, so if there are a lot of imperfections on a given rock it is likely an igneous rock

ie granite

How do sedimentary rocks form?

igneous rocks get broken down by rain and snow , carried by wind and water and end up in small rock pieces in sedimentary beds

ie sand or sandstone

How to tell the age of a sedimentary rock?

the closer to the surface the rock bed is, the newer it is

What causes discontinuity in sedimentary layers?

a fault shift

How do metamorphic rocks form?

eventually as rock layers go deeper and deeper, there is a ton of pressure pushing down from above and it causes the sedimentary rock to turn into a new type of rock that gets baked under high pressure over a long period of time

these very pure rocks are metamorphic rocks (ie a diamond)

How does the rock cycle start over again?

metamorphic rock can get so hot that it becomes igneous again

Weathering can occur by…

chemical means, such as acid rain, or physical means such as wind, rain and ice

What happens when there are a lot of pollutants in the air?

they get rained down and can start to erode or dissolve rocks (ie headstones in highly polluted urban areas experience much more erosion than suburban areas)

What is an example of weathering by physical means?

water gets into rock cracks and freezes, expands, and breaks the rock apart, and this will continue

Weathering generally requires some degree of __________

surface exposure

*if there is a diagram that asks when erosion occurred and you have an eroded layer below a sedimentary layer, most likely the below erosion occurred before the sedimentary layer got deposited.

what is true about smoother landforms?

landforms with smoother contours have generally undergone more erosion and are typically older than angular landforms (ie Great Plains are likely much older than the Swiss alps)

Fossil records can help us determine

the depositional timeline of sedimentary strata (layers) of rock. If we are able to date when a fossil lived and we know it was deposited on a certain sedimentary bed, that tells us that sediment was deposited around the same time.

We can use the known timeline of a sedimentary bed to help us determine…

the dating of fossils within that bed.

What other factors can help us to date rock strata?

weathering, depth, fault shifts & discontinuities can help us date rock strata

Geological Timescale

refers to the vast periods of time over which the Earth changes (millions of years)

Fossil Fuels

created by the compression of biological matter beneath the layers of sedimentary rock, are renewable over a geological timescale, but not over a human timescale (ie oil, coal, natural gas)

Minerals are made of…whereas rocks can be….

one specific chemical composition (may be various elements involved within composition), whereas rocks can be a result of various minerals

Quartz

quartz is a mineral that is part of the rock granite

What are some more examples of minerals?

calcite, hornblende, mica and ores (minerals that contain elements that we want to mine/are useful) such as cassiterite (contains iron to extract for industrial purposes)

What properties can minerals be identified by?

habit, color, luster, hardness, streak

Habit

external shape

Color

color

Luster

shininess

Hardness

determined by the “scratch test” to see if one mineral with a known hardness can scratch the unknown mineral

*this is the most reliable classification when identifying rocks

Streak

when you drag a mineral across a hard surface and some of it powders off, sometimes that powder is different from the surface color, this can determine the two different minerals that look the same as each other

Mohs Scale of Hardness

rates minerals from softest (#1, talc) to hardest (#10, diamond)