ROCKS

T/F Once a rock forms as part of a mountain, it does not change. Some rocks, when exposed on Earth’s surface, undergo weathering and erosion. Large crystals form when lava cools quickly on Earth’s surface. Igneous rocks form when cooling magma crystallizes. Water can dissolve rock. All sedimentary rocks on Earth formed from the remains of organisms that lived in in oceans. With the right pressure and temperature conditions, minerals in a rock can change shape without breaking or melting. Metamorphic rocks have layers that form as minerals melt and then recrystallize.

What is a Rock? Naturally-occurring mixtures of minerals, mineraloids (no crystals), or organic matter.

Some Vocab Deposit – sediment or rock added to a landform Grains – fragments that make up a rock Uplift – The movement that causes rocks that were once underground to be brought up to the Earth's surface.

Types of Rocks… The three main kinds of rock are igneous, sedimentary and metamorphic rock. Igneous rock: forms when magma/lava cools and hardens Sedimentary rock: forms when sediments are buried, compacted & cemented together Metamorphic rock: forms when existing rock is subjected to great heat & pressure over a long period of time

What is the difference between a rock and a mineral? Rocks are made up of ONE or MORE minerals.

Once a rock is formed, does it stay the same rock forever? No Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling Rocks can change to and from the three types

What is the process through which rocks change? The Rock Cycle—earth materials change back and forth among the different types of rocks

How are rocks redistributed? The core, mantle, & crust are one giant rock recycling machine

“Ignis” = Latin for “fire” Igneous Rocks “Ignis” = Latin for “fire” Formed from the cooling of either magma or lava The most abundant type of rock Classified according to their origin and composition Igneous Rocks come from magma/lava cooling down.

Below ground = from magma (intrusive igneous rock) Usually have LARGE crystal grains (they cooled slowly) Cooling could have taken hundreds of years. Above ground = from lava (extrusive igneous rock) Usually have SMALL or NO crystals (they cooled too quickly)

Granite: Intrusive or Extrusive? Why?

Obsidian: Intrusive or Extrusive? Why?

Basaltic Igneous Rocks —made from lava/magma that is low in silica, rich in iron and magnesium. Rocks are dark-colored. Granitic Igneous Rocks—made from magma/lava high in silica and oxygen. Rocks are light-colored.

Sedimentary Rocks Formed from sediments (rock fragments, mineral grains, animal & plant remains-shells, bones, leaves, stems) that are pressed or cemented together or when sediments precipitate (when dissolved materials come out of water) out of a solution.

Sedimentary rocks are fossil-carrying rocks. These sediments are moved by wind, water, ice, or gravity then deposited into layers. Sedimentary rocks represent 7% of the Earth’s crust, but they cover 70% of the Earth’s surface. Sedimentary rocks are fossil-carrying rocks.

What turns sediments into solid rock? Water or wind breaks down and deposits sediment (erosion & deposition) Elements of Erosion are heat, cold, rain, waves, and grinding ice.

At first sediments fit together loosely, over long periods of time, thick layers build up. Because of the heavy layers, the upper layers press down on the layers below them, causing Compaction.

Dissolved minerals flow between the particles and cement them together (cementation)

How can sedimentary layers help us understand the age of fossils? As sedimentary rocks are deposited, they form horizontal layers Scientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.

3 Types of Sedimentary Rocks Clastic – broken pieces of rocks Organic - remains of plants and animals are deposited in thick layers Chemical—minerals dissolved in lakes, seas, or underground water.

Clastic—made of broken pieces of other rocks Clastic—made of broken pieces of other rocks. Formed when rock fragments are squeezed together.

Clastic-Sedimentary Rocks Shale: Formed from tiny particles of clay compacted together. Sandstone: Forms from the compaction and cementation of small particles of sand. Conglomerate: Formed from fragments of various sizes of rocks and pebbles. Fragments are rounded because they have been worn along riverbeds. Breccia: Fragments are jagged with sharp edges. Formed from various size of rocks and pebbles.

3 Types of Sedimentary Rocks: Organic—remains of plants and animals are deposited in thick layers Coal: Remains of swamp plants buried in water or by volcanic ash. Limestone: Formed by hard shells of once living things such as coral, clams, oysters, and snails. When they die their shells pile up and are covered by other sediments compacting and cementing them. (ex. Chalk)

3 Types of Sedimentary Rocks: Chemical—minerals dissolved in lakes, seas, or underground water. Can occur when lakes evaporate. Rock Salt: Made of the mineral halite. Gypsum: Formed by evaporation in dry climates.

Rocks that have changed due to intense temperature and pressure Metamorphic Rocks Rocks that have changed due to intense temperature and pressure “Meta” means “change” and morphosis means “form” in Greek

What occurs in the Earth to change these rocks? Pressure from overlying rock layers High heat, but not enough to melt the rock Rocks may be flattened or bent or atoms may be exchanged to form new minerals.

Where do metamorphic rocks usually form? Where magma intrudes relatively cool rock Near colliding plates (near mountain ranges) Places that are covered miles thick with other rock causing pressure When hot water intrudes rock Where a meteorite strikes Earth (rare) Where lightning bolts strike rocks (rare)

How are metamorphic rocks classified? Foliated—mineral grains are flattened and line up in parallel bands Non-Foliated—No bands are formed

Rocks Transformed Limestone Marble Shale Slate

Rocks Transformed Sandstone Quartzite Gneiss or Mudstone Schist

Say you have an unknown rock how do you classify it? Color: Like with minerals, color alone does not provide enough information to identify a rock.

Say you have an unknown rock how do you classify it? Texture can be very useful. Look at and feel the rocks surface. Some are smooth and glassy others are rough and chalky. Grain Size: Large or Small Grain Shape: Fine Grained or Jagged Grain Patterns: Flat Layers, Wavy, banded, or random. No Visible Grain: Some cool to fast to have grains.

Say you have an unknown rock how do you classify it? Mineral composition: By looking under a microscope, a geologist can identify the minerals it contains. You can use acid to check for carbonates. (Limestone or Chalk)

Say you have an unknown rock how do you classify it? Origin: Where it came from! Metamorphic: Usually have bigger crystals because of increased heat and pressure. Igneous: Usually is made up of very large particles. Sedimentary: Small solid pieces of material that come from rocks or living things. (Smoother)