Rocks Mineral mixtures

What are rocks? All natural rocks are aggregates of minerals The formation of rocks and their physical properties are linked

How and where do rocks form? Many rocks originate from observable processes that take place at the Earth’s surface. Rocks that do not appear to be like surface rocks give us clues to processes active within the Earth.

Rock Classification Rocks are classified according to the processes that form them. Formed by the solidification of magma The breakdown of pre-existing rock Solid state transformation of minerals in a pre-existing rock.

Three types of Rocks Based on the processes of formation three main categories of rocks are recognized: Igneous Sedimentary Metamorphic

Igneous Rocks Crystallized material from molten magma. Volcanic processes = volcanic rocks “Beneath the crust” processes = plutonic rocks Volcanic Rocks = extrusive Plutonic Rocks = intrusive

Cooling of Magma Rapid cooling of magma (extrusive) normally produces rocks with small mineral grains Slow cooling of magma (intrusive) normally produces rocks with large mineral grains

Sedimentary Rocks Deposition and precipitation of materials from the breakdown of older rocks Occurs on Earth’s surface Weathering can be: Chemical – materials dissolve in water Physical – broken fragments (clasts)

Deposition vs. Precipitation Clastic sediments can be lithified (cemented together) to form clastic sedimentary rocks Fragments are cemented with precipitates or simply by compaction Materials dissolved in water will precipitate when conditions are right to form chemical sedimentary rocks

Bedding Sedimentary rocks are recognized by distinctive bedding or layering Bedding is a key feature in recognizing paleo-environments

Metamorphic Rocks Either sedimentary or igneous rocks are transformed by processes occurring within the Earth’s crust. Increased pressure Increased temperature Chemical reactions catalyzed by hot fluids (water most often)

Types of Metamorphic Rocks Regional Metamorphism Affecting vast areas Often at plate boundaries Contact Metamorphism Very localized Occurs adjacent to volcanic or plutonic activity http://www.beavton.k12.or.us/greenway/leahy/00-01/rocks/gneiss.jpg

3. Hydrothermal Metamorphism Hot water flows through the rocks causing a chemical reaction and thus modifying the properties Often causes the precipitation of metal-ore deposits

Minerals found in metamorphic rock depend on the minerals found in the parent rock. And the nature of the metamorphic processes. Similarities in appearance to sedimentary rocks and igneous rocks Bedding and banding at first glace look the same Mineral assemblage appears similar to igneous – generally has more silicates

The Rock Cycle