uniformitarianism: 1795 – James Hutton “the present is the key to the past” we can learn about Earth’s history by studying present processes

What is a rock? rock: an aggregate (group) of minerals

3 Types of Rocks igneous sedimentary metamorphic

Igneous Rock a rock that forms when melted rock inside the Earth cools - formed from volcanic activity

Igneous rocks can form on Earth’s surface or deep inside Earth.

magma: molten rock inside the Earth

intrusive: rocks that form beneath Earth’s surface - mineral grains are clearly seen - form slowly (1000’s of years) ex. granite

extrusive: rocks that form at Earth’s surface - no distinct mineral grains - form relatively quickly ex. obsidian

porphyry: rocks with large crystals surrounded by fine crystals

Families of Igneous Rock

Granite Family - light minerals granite: coarse grained rhyolite: fine grained obsidian: glassy pumice: spongy

Gabbro Family - dark minerals gabbro: coarse grained basalt: fine grained basalt glass: glassy scoria : spongy

Diorite Family: both light and dark minerals diorite: coarse grained andesite: fine grained

Igneous Rocks and the Environment  Intrusive igneous rocks are usually very strong and resist weathering so they make good foundations for large scale construction projects such as dams and buildings (think-granite!)  Sometimes extrusive rocks can be fractured and can cause problems such as cave-ins

Sedimentary Rock a rock that forms from pieces of other rocks or the remains of once- living things - often formed from weathering and erosion

Types of Sedimentary Rocks clastic chemical organic

Clastic Rocks: rocks that form from the weathering of rocks that already exist - most clastic rocks are formed from weathering from running water

Dissolved minerals (natural cements) settle into the spaces between sand grains and pebbles. This “cement” binds the fragments together

Ex. shale, sandstone, conglomerate Sorting of Sediments:

Chemical Sedimentary Rocks rocks that are formed when minerals fall out of solution (when water evaporates or by chemical actions) ex. chemical limestone; rock salt

Organic Rocks rocks that are formed from the remains of plants and animals ex. organic limestone; coal

much of the rock found in this area (PA) is limestone

stratification: arrangement of rocks in visible layers

Sedimentary Rocks and the Environment  Shale and silt can be very weak  Limestone can be cavernous and can cause sinkholes

Metamorphic Rock A rock that is formed when rocks that already exist are exposed to heat and pressure - often formed from mountain building

Regional Metamorphism definition: large areas of rock are under intense heat and pressure

Examples of regional metamorphism: granite  gneiss shale  slate  phyllite  schist

foliation: mineral grains are flattened and lined up in parallel bands layers are easily separated ex. slate

Contact Metamorphism definition: hot magma forces its way into overlying rock and changes it

-no foliation ex. shale  hornfels sandstone  quartzite limestone  marble

Metamorphic Rocks and the Environment  Slate makes excellent foundation material and is also used in pool tables, chalkboards and roofs

THE ROCK CYCLE the process by which Earth materials change to form different types of rocks

Remember…  Rocks become igneous though melting and cooling  Rocks become sedimentary through weathering and erosion  Rocks become metamorphic through heat and pressure