ROCKS

IGNEOUS

Igneous

Sedimentary Metamorphic

The RockCycle

Rocks- naturally occurring combinations of mineral

• 1. Most contain at least 2 minerals.• 2. A few have only 1 • 3. Only 20 minerals are commonly found in

rocks.• James Hutton- first to say that rocks formed

from molten materials, not from minerals crystallized by water as previously thought

• Molten- a solid object formed from liquid material

I. Igneous Rock

• A. Formation of igneous rock– 1. crystallization- as magma cools

below ground, the movement of ions in the liquid slows and the ions arrange into solid, more orderly patterns

– 2. Rate of Cooling- • A. slow cooling deep in the earth forms

very large crystals.

1. Rocks formed in this way are coarse-grained and called intrusive

2. examples: gabbo, granite

b. Faster cooling nearer the surface forms very small crystals 1. Rocks formed in this way are fine-grained and called Extrusive 2. examples: basalt, andesite, rhyolite

C. Instant cooling would result in rocks made of unordered atoms and no definite crystal pattern.

1. These are referred to as glass.

2. examples: obsidian, pumice

• d. When crystallization occurs in areas with much water, unusually large crystals may form.– 1. These are called pegmatites.– 2. They often contain valuable minerals and gems

like beryl and topaz.

3. Composition of Magma

• A. silicon, oxygen, aluminum, sodium, potassium, calcium, iron, and magnesium are the 8 most common mineral materials.

• B. some materials called volatiles (water vapor, CO2) also volatiles- materials commonly found as a gas at surface level temperatures and pressures

c. minerals in magma will crystallize at different rates and temperatures giving igneous rocks varied appearances

4. Igneous textures

• A. texture- describes overall appearance of the rock based on size and arrangement of the interlocking crystals

• B. Texture can reveal details about the environment in which the rock formed.

• 1. Fine-grained textures (called aphanitic) are in igneous rocks formed near the surface– A. individual minerals cannot be identified so

classification is by color-light, intermediate, dark

– B. many can have elongated openings called vesicles through which gases have escaped

– C. igneous rocks formed with this texture are called extrusive

• 2. coarse-grained textures (called phaneritic) are in rocks that form deep in the ground

– A. individual minerals can easily be identified due to the large crystals

– B. igneous rocks formed with this texture are called intrusive

• 3. Some igneous rocks begin to cool deep below surface, then get brought upward to finish cooling more quickly

– A. they have some large crystals and some very small ones

– B. these have porphritic textures, with the large crystals called phenocyrsts and small ones called groundmass

4. Glassy textures

• A. form when magma is thrown upward during eruptions which cool them instantly

• B. example: obsidian- looks like a dark chunk of man made glass, used in Native American arrowheads pumice- very light –weight rocks that have many vesicles and can float on air or water

Floating pumice

• 5. pyroclastic textures- igneous rocks that have pieces of ash, or other molten blobs imbedded in them. Ex: tuff

B. Bowen’s Reactive Series

• 1. Shows the exact order in which minerals form as magma cools (depends on depth and elements present)

Pg. 73

2. Sequence descriptions

• A. olivine and pyroxene form first, are rich in iron and magnesium, and are very dense

• B. igneous rocks that contain these dense minerals are called mafic rocks and are usually black or dark green– 1. they form from magma ~ 900º C (1620º F) -

1200ºC (2160ºF)– 2. ex: basalt- makes up most of ocean bottom,

gabbro-found on many Pacific Islands

• C. igneous rocks that contain low-density minerals are called felsic and are light colored.

– 1. they form from magma about 800ºC (1440º F)

and contain quartz and feldspar minerals

– 2. ex: andesite, rhyolite, and the most common rock of all *granite*

Uses of Igneous Rock

• 1. Carvings and inscriptions made in granite can withstand weathering– Ex. Vietnam Veteran’s Memorial wall in

Washington, D.C.

• 2. Pumice is ground up and used as a scouring powder

• 3. Some igneous rocks have valuable minerals like iron, copper, and uranium mixed in.