ROCK NOTESROCK NOTES

I. What is a rock?

Rock - two or more minerals (found in the earth’s crust) bound together in a solid form

II. Rock types

A. Sedimentary rocks- formed by the hardening and cementing of layers of sediment.

II. Rock types

B. Metamorphic rocks- formed when rocks that already exist are changed by heat and pressure into new kinds of rocks.

II. Rock types

C. Igneous rocks- formed by cooling and hardening of hot molten rock from inside the Earth. Hot molten rock from inside the earth is called magma.

III. Igneous Rock Formation

A. Magma - molten (liquid) rock found beneath the earth’s surface. Intrusive Rock - rock formed underground when magma cools

III. Igneous Rock Formation

A. From Magma (Intrusive )

Cooled slowly

Deep Shallow

Large/Coarse Small Crystals Crystals

III. Igneous Rock Formation

B. Lava - magma on the surface of the earth Extrusive Rock - rock formed on the surface when lava cools

III. Igneous Rock Formation

B.From Lava (Extrusive)

Cooled quickly

Surface

Fine Crystals Glassy Rocks

IV. Igneous Rock CharacteristicsA. Felsic (feldspar and silica--Granitic, Continental)

• Chemistry: High percent of silicates (Si) and water. Low percent of iron (Fe), calcuim (Ca), & magnesium (Mg)

• Color: Light colored minerals

• Viscosity: More viscous (Thick--Low temperatures and slow flowing)

• Trapped gases: H2O, O, CO2, H2, CO, H2S, SO2

• Density: Low level (high gas content)

IV. Igneous Rock CharacteristicsB. Mafic (Magnesium and iron--Basaltic, Oceanic)

• Chemistry: Low percent of silicates (Si). High in Ca, Fe, Mg.

• Color: Dark colored minerals

• Viscosity:Low viscosity (thin--high temperature and more fluid)

• Trapped gases: fewer present

• Density: Higher level (few gases)

IV. Igneous Rock CharacteristicsC. Andesitic (Intermediate, Continental)

• Chemistry: Intermediate percent of silicates (Si). Intermediate in Ca, Fe, Mg.

• Color: Intermediate colored minerals

• Viscosity: Intermediate viscosity (fluidity)

• Trapped gases: Intermediate amounts present

• Density: Intermediate level

IV. Igneous Rock Characteristics (D. Review)

A. Felsic B. MaficMostly light Mostly dark

colored minerals colored minerals

[ Si] [Ca, Fe, Mg] [ Si] [Ca, Fe, Mg]

C. Andesitic

Contain light and dark minerals

Intermediate levels of [Si, Ca, Fe, Mg]

IV. Igneous Rock Characteristics (D. Review)

A. Felsic Dissolved B. Mafic Dissolved Gases Gases

Thick & Slow Thin & Fast

Hard For Gases Gases Escape To Escape Easily

Explosive Eruptions “Gentle” Eruptions

Note: Dissolved Gases Include H2O, S, CO2, H2, CO, H2S, SO2

IV. Igneous Rock CharacteristicsD. Review

Extrusive

IntrusiveSmall crystals

Large crystals

IV. Igneous Rock Characteristics (D. Review)

NO crystals

Darker colored rocks

Lighter colored rocks

V. Plate Tectonics and Igneous Rocks

VI. How we study rocks

A. Color: Lightness/darkness indicates chemistry. Darker rocks tend to have more iron (Mafic), lighter rocks have more silicon (Felsic).

B. Crystal size: Can be measured in millimeters using a hand lens/microscope and ruler. Larger crystals need more time to form and are found in rocks that cool slowly (intrusive).

Small crystals

Large crystals

Fine crystals

Felsic

Andesitic Mafic

VI. How we study rocks

C. Density: mass (g) ÷ volume (ml or cm3).

More dense rocks formed from magma that originates deeper in mantle (less explosive volcanoes) and contain

fewer gases (Mafic).

Less dense rocks formed from magma that originates from outer mantle (more explosive volcanoes) and contain more trapped gases due to interaction with ocean water (Felsic).

=(C4/D4)