Volcanoes in our Community Volcanic and Other Types of Rocks and What Makes Them Science Std: Geo # 3c

There are 3 main types of rocks  Sedimentary  Metamorphic  Igneous

Melting There are 3 main types of rocks  These rocks all change from one type into another Sedimentary Rock Metamorphic Rock Igneous Rock Sediment Silt and Dirt Sediment Silt and Dirt Lava and Magma Pressure Weathering Pressure Weathering Heat and Pressure Melting Cooling Melting

All rocks are made from….  Minerals that can be described by….  A Chemical Formula Each mineral has a unique (only one) combination of atoms  How it Looks And Acts Porous (lots of tiny bubble holes called vesicles Granular (lots of small grain parts) Smooth / Rough Hard / Soft Shiny / Dull How easily it breaks

All rocks are made from….  All Minerals have Crystals Crystals are atoms and molecules that are grouped and stuck together in a neat pattern Like toy soldiers lined up, they have a definite pattern that keeps going on and on We’ll talk more about crystals later….

Let’s look at the 3 types of rocks  How are they formed and look Sedimentary Rock Metamorphic Rock Igneous Rock First we will look at Igneous Rocks

Lets look at the 3 types of rocks  Molten rock (magma and lava) cools and makes Igneous Rock Sedimentary Rock Metamorphic Rock Igneous Rock First we will look at Igneous Rocks  Depending on how fast it cools, it looks very different  If it cools fast, it makes small crystals that you can’t see  If it cools slowly, it has time to make big crystals that you can easily see

Lets look at the 3 types of rocks  There are 2 main types of igneous rocks Igneous Rock  Extrusive or Volcanic igneous rocks They cool quickly Normally come to the surface Little or no crystals seen in the rocks (Basalt) Very few crystals makes the rock look like black glass (Obsidian) Basalt Igneous Rock Obsidian Igneous Rock

Lets look at the 3 types of rocks  There are 2 main types of igneous rocks Igneous Rock  Intrusive or Plutonic igneous rocks Cools slowly under the surface of the Earth Big crystals formed easy to see with eye Sizes and shapes vary widely from boulders to whole mountain ranges Can only see when lifted up or erosion shows them Granite Geode Quartz Diamond

Lets look at the 3 types of rocks  Regardless of the type of rock…. Igneous Rock  The color of the rock depends on the minerals in the magma Light colored rocks have high silica content Darker colors are from iron and magnesium Medium colored rocks have combinations of light and dark minerals Dark colored rocks have low silica content and have more iron and magnesium

Sedimentary Rock Lets look at the 3 types of rocks  The next type of Rock is Sedimentary Igneous Rock  There are 3 types of sedimentary Sandstone Made from sediment only Limestone Made from pieces of fossils and sediment Conglomerate Made from other bits of rock and sediment

Metamorphic Rock Sedimentary Rock Lets look at the 3 types of rocks  The last type of rock is Metamorphic  These can be made by….. Heat alone This is where the rocks are heated and changed without having a lot of pressure on them Heat and Pressure This is where there is both heat and a large amount of pressure to change the rocks Limestone Becomes Marble

Igneous Rock Metamorphic Rock So where can these rocks form?  Igneous rocks come from volcanic events  But you don’t have to have an eruption to make igneous rocks….. Magma Pockets Magma can rise up and collect in a pocket The magma can cool and form igneous rocks It cools slowly so it can make large crystals Lava on the surface Lava comes to the surface On the surface it is quickly cooled by air or water So it forms small crystal rocks

Metamorphic Rock Igneous Rock So where can these rocks form?  Metamorphic rocks form primarily at plate boundaries. Convergent Plates 2 plates crush and rub together High pressure and temperatures change the rocks They can then work their way up or we can dig down Transverse Plates 2 plates rub together Harder to do here because you need heat to have the change Unless the transverse boundary is deep, you won’t get the heat needed

Sedimentary Rock Metamorphic Rock So where can these rocks form?  Sedimentary Rocks usually form under water Sand and silt pile up on the ocean floor Over time (millions of years) the silt on the top presses down on the silt on the bottom After a long time, the silt on the bottom presses and cements together into new sedimentary rocks

Sedimentary Rock Metamorphic Rock Where do the rocks go? All rocks erode and wear away due to water and weather and chemical action Rocks are subducted at convergent plate boundaries and are melted back into magma Rocks under the surface can break apart (fracture) speeding up the erosion Igneous Rock Eventually, all rocks are recycled into another type of rock