Thursday, October 4 th Objective: We will use and define the different ways to classify igneous rocks. Warm-up: 1. Which type of lava is most viscous? 2. Which type of lava has the least amount of silicate? 3. What type of volcano is shown here? How did it form?
Igneous Rocks Hot rocks/fire Rocks
Rock Lab Establish lab groups One person grabs the rock kit Lab 1 Remove rocks 4,5, 7, 10, 11, 12, and the no number one. Group the rocks how you see fit. Record groupings with reasons, in notebook (left side)
Rock Lab Lab 2 Use rocks 4,5, 7, 10, 11, 12, and the no number one. Group the rocks a different way. Again, record groupings and reasons.
Igneous Rock Igneous rocks form when molten rock cools and solidifies. Molten rock is called magma when it is below the Earth s surface and lava when it is above.
Crystal size when molten rock cools and solidifies Magma (below) Lava (above)
Igneous Rock classification Igneous rocks are classified two different ways: Where they were formed What they are made from (mineral composition)
Part 1 Classifying igneous rocks by where they are formed.
Intrusive Igneous Rocks Igneous rocks that form below the Earth s surface are called intrusive igneous rocks (or plutonic). The word plutonic comes from Pluto, the name for the Greek god of the underworld. They form when magma enters a pocket or chamber underground that is relatively cool and solidifies into crystals as it cools very slowly.
Crystal size magma Intrusive slowly large when molten rock cools and solidifies Magma (below) Lava (above)
Intrusive Igneous Rock Granite Gabbro Diorite Most intrusive rocks have large, well formed crystals. The mineral crystals within them are large enough to see without a microscope. The more slowly molten rock cools within the Earth, the larger the igneous rocks crystals will be. Examples of intrusive igneous rocks are granite, gabbro and diorite
Crystal size magma Intrusive slowly large Granite, gabbro, diorite when molten rock cools and solidifies Magma (below) Lava (above)
Extrusive Igneous Rocks Extrusive igneous rocks, or volcanics, form when magma makes its way to Earth's surface. The molten rock erupts or flows above the surface as lava, and then cools forming rock. Most extrusive (volcanic) rocks have small crystals. Examples include basalt, rhyolite, and andesite.
Location of Extrusive Rocks Convergent Boundary (73%) Subduction Zone Divergent Zone (15%) Mid-oceanic Ridge Hot Spots (12%)
Crystal Animation Animation
Crystal Size
Lava Quickly Crystal size Small or not visible Pumice, obsidian, basalt Extrusive magma Intrusive slowly large Granite, gabbro, diorite when molten rock cools and solidifies Magma (below) Lava (above)
Volcanic Glass Pumice, obsidian, and scoria are examples of volcanic glass. These rocks cooled so quickly that few or no mineral grains formed. Most of the atoms in these rocks are not arranged in orderly patterns, and few crystals are present.
Glassy Igneous Rocks Glassy Igneous Rocks cool so rapidly, that atoms don t have enough time to get together, bond and form crystals. To cool this quickly the rocks MUST be extrusive. Pumice (left) Scoria (bottom left) Obsidian (bottom) Note gasses in the lava can cause fine holes called vesicles as seen in the pumice and scoria.
Part 2 Classifying by mineral composition
Magma types A way to further classify these rocks is by the magma from which they form. An igneous rock can form from, felsic, intermediate, or mafic magma. Magma composition determines the physical & chemical properties of an igneous rock
Lava Slowly Crystal size felsic Small or not visible Physical & chemical properties Pumice, obsidian, basalt Extrusive Intermediate magma Intrusive slowly large Granite, gabbro, diorite when molten rock cools and solidifies Magma (below) Lava (above) Mafic *SiO 2 = Silicon Fe = Iron Mg = Magnesium
Mafic Igneous Rocks Mafic igneous rocks are dense, dark-colored rocks. They form from magma that is rich in iron and magnesium and poor in silica, which is the compound SiO 2. The presence of iron and magnesium in minerals in Mafic rocks gives them a dark color. Mafic lava is fluid and flows freely from volcanoes in Hawaii, such as Kilauea. Basalt (a mafic rock) is the most common rock type in the Earth's crust (the outer 10 to 50 km). In fact, most of the ocean floor is made of basalt
Mafic Igneous Rocks Oceanic Plates are made primarily of Mafic rocks. Explains why they are thinner but more dense
Lava Slowly Crystal size Felsic Small or not visible Physical & chemical properties Pumice, obsidian, basalt Extrusive Intermediate magma Intrusive slowly large Granite, gabbro, diorite when molten rock cools and solidifies Magma (below) Lava (above) Mafic Rich in Fe & Mg poor in SiO 2 Dense & dark colored Ocean floor & Hawaii
Felsic Rocks Felsic igneous rocks are light-colored rocks of lower density than basaltic rocks. Felsic rocks are coarse-grained Felsic magma is thick and stiff and contains lots of silica but lesser amounts of iron and magnesium. It is the most common rock type on the continental land masses. Yosemite Valley in the Sierra Nevada and Mt. Rushmore are two notable examples of granitic rocks
Felsic Rocks Continental plates are primarily made of felsic rocks. Explains why they are thicker and less dense.
Lava Slowly Crystal size Felsic High SiO 2 Low Fe & Mg Light colored, less dense Small or not visible Physical & chemical properties On the continents Pumice, obsidian, basalt Extrusive Intermediate magma Intrusive slowly large Granite, gabbro, diorite when molten rock cools and solidifies Magma (below) Lava (above) Mafic Rich in Fe & Mg poor in SiO 2 Dense & dark colored Ocean floor & Hawaii
Intermediate Rocks Intermediate igneous rocks have mineral compositions between those of felsic and mafic rocks. Many volcanoes around the rim of the Pacific Ocean formed from Intermediate magmas. Like volcanoes that erupt felsic magma, these volcanoes also can erupt violently. Rocks made from intermediate magma tend to be fine-grained.
Lava Slowly Crystal size Felsic High SiO 2 Low Fe & Mg Light colored, less dense Small or not visible Physical & chemical properties On the continents Pumice, obsidian, basalt Extrusive Intermediate b/t basaltic & granitic Grey, medium magma Intrusive Pacific Rim slowly large Granite, gabbro, diorite when molten rock cools and solidifies Magma (below) Lava (above) Mafic Rich in Fe & Mg poor in SiO 2 Dense & dark colored Ocean floor & Hawaii
Igneous Rock Classification Table Felsic (light colored) Intermedi ate Mafic (dark colored) Ultramafic Coarse (Intrusive) Fine (Extrusive) Vesicular-lots of holes (Extrusive) Glassy (Extrusive) Granite Diorite Gabbro Peridotite Rhyolite Andesite Basalt Pumice Pumice/ Scoria Obsidian Scoria
P age 11b (yesterday s notes) 1. Which of the following is not a way that igneous rocks are classified? a. Chemical Makeup b. Color c. Location of Formation d. Size 2. What type of rock is shown at the right? How did it form? 3. How are rocks with large crystals formed?
Quick Questions 2. How are course-grained rocks formed?
Quick Questions 3. What type of igneous rock is shown below? How did it form?
Page 12a or 12b (still) Do not use notes! 1. What are the two ways to classify igneous rocks? 2. How does location of formation affect rock properties? 3. How does lava type affect rock properties?
Quick Questions (QQ) 1. Was the lava this rock was made from runny or thick?
Quick Questions (QQ) 2. Did this rock cool quickly or slowly?
Quick Questions (QQ) 3. Based on location, what type of rock is this?
Quick Questions (QQ) 4. What is the chemical composition of this rock?
Quick Questions (QQ) 5. What is the name of this rock?