The Rock Cycle

The Major Rock Types

Igneous

Sedimentary

Metamorphic

Magma

Any of these rock types can be converted into other rock types via the Rock Cycle

Igneous Rock (Magma → Igneous)

Root word: ignite

Comes from lava/magma. That molten rock is under the earth’s surface, it’s called magma.

When it erupts through a volcano and reaches the Earth’s surface, we call it lava

It’s name changes when it reaches the Earth’s surface

Magma or Lava Harden

When lava comes out to the Earth’s surface, it can be underwater in underwater volcanoes or it can be above ground.

Either way, when it hits water or cool air it hardens very quickly.

They tend to have lots of impurities

Are Magma and Lava the same thing?

No, magma and lava are not exactly the same thing, although they are both molten rock; the key difference is location: magma is molten rock beneath the Earth's surface, while lava is magma that has erupted onto the surface. 

Rule of Thumb of Igneous Rocks

Rocks that have a lot of impurities and speckling, are often Igneous Rocks.

Igneous Rocks and Weathering (Rock man Vs. Weatherman)

Wind, rain, and ice can break down rock over time into smaller and smaller pieces.

Eventually, pieces (clast) get carried away by the wind, rivers, and more.

They are deposited in Sedimentary Rock beds.

Sedimentary Rock

Small pieces of igneous rock (clast) get carried by rock wind and rivers, and more get deposited into _____ rock.

Slowly, layer by layer, pieces of clast are bonded by mineralized water to create ______ rock

Dating Sedimentary Rock Beds

Newer rock layers form on top of older ones. The deeper a layer is, the older it is.

Sometimes, rock layers shift and don’t line up anymore. This means a fault moved them after they were formed, creating a discontinuity (a break in the layers).

discontinuity

is a break or gap in rock layers that happens when the layers shift, tilt, or erode over time.

It shows that something like an earthquake, fault movement, or erosion changed the original order of the layers after they were formed.

Sedimentary Rock to Metamorphic Rock

as rock layers get deeper and deeper, there’s a tremendous amount of pressure pushing down from above

It causes sedimentary rock such as sand/sandstone to clasticize (turn into a new rock)

that gets baked under high pressure over a long period of time.

These rocks tend to be very pure and are called _____ rock

Metamorphic

changed by heat and pressure

Sedimentary Rock to Metamorphic Rock (magic school bus)

two pieces of earth’s crust aka tectonic plates squeeze rock together while its being cooked by the heat of the stuff under the crest.

Over 1-2 million years, pressure from the tectonic platers and heat created _______ rock.

Metamorphic Rocks

Rocks that get baked by pressure underground for over long periods of time is metamorphic rocks.

e.g.

Diamonds

Eventually, metamorphic rocks can get so hot and heat up they become igneous

Any of the rock types can become

other rock types

Weathering and Chemical Erosion Affecting Stones

Can occur by chemical means such as acid rain or physical means which is wind, rain and ice

When lots of pollutants in the atmosphere, those get brought down with the raindrop droplets they can start to dissolve or rocks

Weathering and Chemical Erosion Affecting Stones Example

Headstones in highly polluted urban areas and then look at headstones and areas where there’s not much pollution because chemicals and atmosphere brought down by rain

Physical Effects to Rocks (weathering)

Rain, ice, or wind that happens over millions of years

• Water can go into cracks of rocks and freeze; when it freezes, it expands and breaks the rock apart a little bit. More water pours into the water freezes breaks again

• Wind pushing over it breaks into small pieces and wears smooth over time

• Water running over it, breaks into small pieces and wears smooth over time

Erosion on a Diagram (Top to Bottom Layers)

Weathering requires some degree of surface exposure

e.g.

Eroded layer on bottom instead of layer on top. Most like bottom layer occurred before sedimentary layer was deposited.

Because if it was deep underground, those agents of erosion wind, rain, and ice, wouldn’t be able to reach it

Landforms w/ Smoother Contours (weathering)

Landforms with smoother contours have generally undergone more erosion and typically older than angular landforms

• the more eroded the smoother it is

• Smoother = older

E.g. The great plains, geologically, older than the Swiss Alps. Protrusive, angular landforms, have not experienced much erosion, geologically, their much newer.

Determining Timeline - Fossil Records

This can help us determine the depositional timeline of the sedimentary strata of rock

• Able to date when a fossil lived, we’d know it was deposited in a certain sedimentary bed

• It also tells us that sediment must have gotten around that same time

Likewise, when we can all fossil deposit that those organisms must’ve also lived around the same time

Other Factors Help Us Determine Timeline

• Weathering

• Depth,

• Fault Shifts,

• Discontinuities)

  All these help us date rock strata

Other Factors Help Us Determine Timeline 1.Weathering

If Strata been weathered, most likely happened when exposed to the surface

Other Factors Help Us Determine Timeline 2. Depth

Tells us relative age. Deeper it is, the older it is because new layers get deposited on top of the old layer.

Other Factors Help Us Determine Timeline: 3. Fault Shifts

Discontinuities, layers used to line up now shifted so fault occurred after deposition

Geologic Timescale

Refer to the vast periods of time over which the Earth changes

This along with other processes occur over millions and millions of years, not overnight

Fossil Fuels

Created by the compression of biological matter beneath the layers of sedimentary rock

Things alive many years ago, get buried underground. Many layers of sediment get deposited on top and eventually that causes that biological matter to become

• oil,

• coal,

• and sometimes when gaseous, natural gas.

Eventually, everything alive today will become oil, but not renewable over human timescale

Minerals

Made up of one specific chemical composition

• Although there may be various elements involved, it’s specific chemical composition

Whereas rocks can be aggregate a various minerals

• chunks of different minerals aren’t chemically combined, they’re just chunk together

Strata

Layers

Quartz

A mineral that’s part of granite

e.g.

Granite has all these little speckles of different things in it. Lots of stuff in it, but that’s one of the things is the MINERAL QUARTZ

• Diff shapes, but still a single chem compound

Ores

Contain minerals or elements and things we want to mine

• they’re useful to us

  e.g. Cassiterite- ores contains iron and it’s mined to extract iron

Minerals Identified by Various Proeprties

• Habit,

• Color,

• Luster,

• Hardness

• Streak

Habit

external shape of that mineral. Different types of minerals take on different kinds of physical external shapes.

Color:

what’s the color look like?

Luster

shininess of the mineral

Hardness

Test, with mineral of known hardness. Can known scratch unknown?

Streak

• Drag mineral across hard surface and some powders off.

• Sometimes that powder is different color than the color.

• The mineral appears before you’ve staked it and created that powder.

• The color appears as well as the color that powder appears after streak test can help differentiate between two minerals that externally looks similar until you’ve done the streak test

Chemical Reactions Related Rocks and Minerals (Limestone)

Limestone: Calcium Carbonate

Calcium Carbonate is a base

Vinegar poured onto limestone dilutes acetic acid

• When we combine bases and acids, a chemical reaction occurs.

We see evidence of that reaction because you’ll see vinegar bubbling on the limestone, and heat comes off evidence of chemical reaction

• When acids and bases undergo a reaction, what gets created is water and salt (Calcium Acetate)

Calcium Acetate and Mineral and Rocks Useful to Humans

• Salt created by pouring vinegar onto limestone

  • We’ve caused a chemical reaction that results in water and calcium acetate

Another way to look at rocks and minerals and another in which things can be transformed in ways that are useful to humans

• e.g., Calcium Acetate is salt, a common food additive