Rocks & the Rock Cycle Rocks & the Rock Cycle

Minerals and rocks are stable only under the conditions at which they form. Change the conditions and the rocks will change to adapt to the new conditions. The underlying principle for understanding all things geological is:

Rock - an aggregate of one or more minerals Mineral (review) – Naturally occurring inorganic solid materials with definable chemical compositions and an orderly arrangement of atoms within a lattice. Let’s start at the very beginning…

Three main rock types ~ Igneous ~ Sedimentary ~ Metamorphic Let’s start at the very beginning…

Pyroclastic material Lava Igneous Part of the Rock Cycle

Igneous Rocks All igneous rocks –cool and crystallize from magma (inside) –or solidify from lava (outside) –or consolidate from pyroclastic materials (outside) Magma is molten material below the surface Lava is molten material on the surface Pyroclastic materials –particles such as volcanic ash, volcanic bombs, tephra, etc.

Classification of Igneous Rocks Igneous rocks are classified by composition and texture. Composition = what it’s made of Texture = how it’s put together.

Composition Composition – These categories are based on silica content. “Granitic” igneous rocks - (AKA - Felsic igneous rocks) Light-colored igneous rocks made from felsic (light-colored) minerals such as quartz, micas, and feldspars. “Basaltic” igneous rocks - (AKA - Mafic igneous rocks) Dark-colored igneous rocks made of mostly mafic minerals such as olivines, pyroxenes, amphiboles, and Calcium-rich plagioclase. The terms the book uses for these rocks (Granitic and Basaltic) are a poor choice, as we will see….

Texture Extrusive (“outside earth”) – cools quickly to instantaneously. Crystals do not have time to grow to visible size. formed at the surface from lava or pyroclastic materials Example: Basalt, Pumice Intrusive (“inside earth”) – cools slowly over loooooong periods of time, allowing crystal growth to occur. Produces crystals visible to the naked eye. formed below the surface Example: Granite Texture - the size, shape and arrangement of crystals, grains and other components of the rock. Texture is controlled by the rate of cooling and crystallization. So why are the book terms of “Granitic” and “Basaltic” not good terms to use?

Differences in Texture Extrusive texture Rapid cooling Intrusive texture Slow cooling Vs.

Extrusive Textures Glassy texture Extremely fast cooling Vesicular texture Created by escaping gasses trapped in cooling lava

Rainbow Obsidian The iridescent, rainbow-like sheen of rainbow obsidian is caused by inclusions of magnetite nanoparticles. Say what? Tiny pieces of the mineral magnetite are trapped in the molten rhyolite magma when it cools very fast. Spear tips made from rainbow obsidian

Common Intrusive Igneous RocksGabbro Felsic Mafic Composition Granite Slow cooling magma allows crystals to grow to visible size

Common Extrusive Igneous Rocks Mafic Felsic Composition Rhyolite Fast cooling, typically in the form of lava, prevents crystals from growing to a visible size Basalt

Extrusive texture (cooled quickly) Felsic composition (light in color) When rhyolite lava cools extremely quickly, it forms obsidian. Rhyolite

Intrusive texture (slow cooling) Felsic composition (light in color) Slow cooling allows the crystals time to grow to a visible size Granite

Vesicular texture (fast cooling) Scoria Holes are produced by gas escaping rapidly as it cools.

Glassy texture (cooled extremely fast) Obsidian

Cooling Rate = ? Composition = ? Texture = ?

Cooling Rate = ? Composition = ? Texture = ?

Cooling Rate = ? Composition = ? Texture = ?

Cooling Rate = ? Composition = ? Texture = ?

Cooling Rate = ? Composition = ? Texture = ?

Cooling Rate = ? Composition = ? Texture = ?

Cooling Rate = ? Composition = ? Texture = ?

Famous Igneous Rocks!!

Igneous rocks - Review Igneous rocks – form from cooled molten rock Magma Lava Textures – 2 types, know how each type forms Extrusive Intrusive Composition – 2 types Felsic Mafic

SedimentaryRocksSedimentaryRocks

Sediment Loose particulate material or residue (clay, sand, gravel, etc.) from a specific source (biochemical, chemical, detrital). Sediment is created through the process of weathering… Weathering Transport Uplift Deposition Lithification TheSedimentaryCycleTheSedimentaryCycle

Weathering = Making sediments Two types of weathering: Chemical – decomposing or dissolving of Earth material Physical – cracking, scratching, abrasion, or other physical breaking up of Earth material (clasts, rock fragments, mineral grains from inorganic sources; peat, shell gravel from organic sources) Weathering Transport Uplift Deposition Lithification The Sedimentary Cycle

Chemical Weathering

Physical Weathering

Weathering

Transport Moving sediments from where they were formed to where they are deposited Transported by wind, water, and/or ice

Transport by Wind

Transport by Water

Transport by Ice

Deposition Sediments are ‘deposited’ somewhere like a lake, river, or other area where the wind, water, or ice will not move them any further.

Alluvial Fans

Braided Stream

Deltas

Meandering Rivers

Lithification = “Turned to stone” Once deposited, sediments turn to sedimentary rocks by one or more of these processes: Compaction Cementation Precipitation / Evaporation

METAMORPHIC ROCKS “Change of form”

MetamorphicRocksMetamorphicRocks

Metamorphic rocks are formed when heat and pressure changes another rock The rock that is changing does not melt during metamorphosis What would we call it if it did melt?

Metamorphic rocks can be formed from:  Igneous rocks  Sedimentary rocks  Other metamorphic rocks What can be changed?

Metamorphic Rock Classification Metamorphic rocks are broken out into two main groups, foliated and non-foliated. Foliated – Have bands of different colored minerals Non-foliated – No layering or banding present

Where on Earth?

The Rock Cycle – A Different View