ROCKS

What is a Rock? Naturally-occurring mixtures of minerals, mineraloids, glass or organic matter.

What is a Rock? Rocks are divided into 3 groups based on how they were formed: IGNEOUS SEDIMENTARY METAMORPHIC

What is the difference between a rock and a mineral? Rocks are made up of ONE or MORE minerals.

Once a rock is formed, does it stay the same rock forever? NO!

Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling Rocks can change to and from the three types

What is the process through which rocks change? The Rock Cycle—earth materials change back and forth among the different types of rocks

IGNEOUS METAMORPHIC SEDIMENTARY Weathering, Erosion, Compaction, Cementation Recrystallization Melting, Solidification Melting, Solidification Recrystallization SEDIMENTARY METAMORPHIC Weathering, Erosion, Compaction, Cementation

The core, mantle, & crust are one giant rock recycling machine

“Ignis” = Latin for “fire” Igneous Rocks “Ignis” = Latin for “fire” Formed from the cooling of either magma or lava The most abundant type of rock Classified according to their origin and composition

ORIGIN— Where rocks are formed Below ground = intrusive rock, made from cooling of magma Usually have coarse (large) crystal grains because they cooled slowly.

Above ground = extrusive igneous rock, formed from cooling of lava Usually have fine (small) or even NO crystals because they cooled fast!

#7 Granite: Intrusive or Extrusive? Why? Intrusive! It is coarse-grained with large crystals, thus cooling slowly.

#1: Obsidian: Intrusive or Extrusive? Why? Extrusive! It is fine-grained, no crystals and glassy luster indicate fast rate of cooling.

#3 Scoria: Intrusive or Extrusive? Why? Extrusive! Air pockets indicate fast rate of cooling, exposure to air.

#4 Basalt: Intrusive or Extrusive? Why? Extrusive! It is fine-grained with very small crystallization.

Practice Classifying Igneous Rocks as intrusive or extrusive— Take out & classify these rocks from your kits. Examine the texture and determine if they are coarse-grained (large crystals) or fine-grained (small or no crystals). Make two piles!

Mafic (Basaltic) Igneous Rocks Made from lava/magma that is low in silicate minerals, rich in iron and magnesium. Rocks are dark-colored.

Felsic Igneous Rocks—made from magma/lava high in silica and oxygen (like the mineral, quartz). Rocks are light-colored.

#4: Basalt Mafic! High mineral content of olivine and hornblende; both heavy, dense minerals.

#2: Pumice Felsic! Light color indicates silicate minerals.

Practice Classifying Igneous Rocks according to their composition: Felsic or Mafic? Make two piles!

#10: Diorite: Felsic or Mafic? Considered “Intermediate” because it has almost equal amounts of plagioclase (gray feldspar) and hornblende!

Sedimentary Rocks Formed from sediments that include rock fragments, mineral grains, animal & plant remains Sediments erode from bigger rocks due to mechanical or chemical weathering.

Sedimentary Rocks These sediments are moved by wind, water, ice or gravity. Sediments lay down on Earth’s surface in a process called “deposition”. Sediments compact and cement together or precipitate (make solid) out of a solution

The heavy sediments press down on the layers beneath Compaction The heavy sediments press down on the layers beneath

Cementation Dissolved minerals flow between the particles and cement them together

How were most of the sedimentary rocks in Ohio deposited? Continental glacier Ancient seas

How can sedimentary layers help us understand the age of fossils? As sedimentary rocks are deposited, they form horizontal layers Scientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.

Types of Sedimentary Rocks: Clastic: made of broken pieces of other rocks or shells cemented together Coquina Conglomerate Sandstone Breccia

Types of Sedimentary Rocks: Chemical—minerals dissolved in lakes, seas, or underground water

Examples Limestone made when calcite mineral precipitates from sea water Rock Salt—made from evaporation of sea waters

Types of Sedimentary Rocks: Organic—remains of plants or animals are deposited in thick layers Examples: Fossil rich limestone is made from the shells of ocean animals; used to make chalk Shale and coal

Clastic, Chemical, or Organic? #16 Conglomerate CLASTIC

Clastic, Chemical or Organic? Bituminous Shale (black because of the remains of plants) #20 CLASTIC AND ORGANIC

Clastic, Chemical, or Organic? #23 Travertine CHEMICAL

Separate your sedimentary rocks by making two piles, one pile of Clastic rocks, and the other pile of Chemical rocks!

Rocks that have changed due to intense temperature and pressure Metamorphic Rocks Rocks that have changed due to intense temperature and pressure “Meta” means “change” and morphosis means “form” in Greek Igneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks

Regional Metamorphism Tectonic plates push into each other above and below the surface of the Earth Enormous pressure on rock that is buried under other rock formations; makes foliated (banded) rock.

Contact Metamorphism Heat, but not enough to melt the rock, comes from contact with magma bodies and re-crystallizes minerals; Makes non-foliated rock. Note the white marble on the mountainside.

How are metamorphic rocks classified? Foliated—mineral grains are flattened and line up in parallel bands Example: gneiss formed from rearrangement of minerals in granite into bands

How are metamorphic rocks classified? Non-Foliated—No bands are formed Minerals break bonds and re-crystallize Quartzite Below: marble formed from limestone

Separate your metamorphic rocks into two piles, one pile of foliated rock caused by regional metamorphism, and the other pile of non-foliated rock caused by contact metamorphism!

Where do metamorphic rocks usually form? Where magma intrudes relatively cool rock Near colliding plates (near mountain ranges) Places that are covered miles thick with other rock causing pressure When hot water intrudes rock Where a meteorite strikes Earth (rare) Where lightning bolts strike rocks (rare)