Rocks & the Rock Cycle

The underlying principle for understanding all things geological is: 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.

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

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

Igneous Part of the Rock Cycle Pyroclastic material Lava Igneous Part of the Rock Cycle Igneous part of rock cycle is constructive force, creating new crust and or rocks.

Magma is molten material below the surface 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 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. 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 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.

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

Spear tips made from 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 Rocks Granite Slow cooling magma allows crystals to grow to visible size Gabbro Felsic Mafic Composition

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

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

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

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

(cooled extremely fast) 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

Sedimentary Rocks

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

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”

Metamorphic Rocks

The rock that is changing does not melt during metamorphosis 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: What can be changed? Metamorphic rocks can be formed from:  Igneous rocks  Sedimentary rocks  Other metamorphic rocks

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