I. Igneous
Use these notes to sort the igneous rocks as extrusive and intrusive. Then identify each rock using the notes below.
A. Extrusive
1. Pumice and Scoria are created as volcanoes shoot out gas and lava. The lava mixes with the gas so the gas is trapped as the lava cools. After a while the gas escapes leaving holes. Pumice is lighter colored than Scoria.
2. Tuff is a fine crystal rock, light colored that is formed from the ashes that are blown out from volcanoes.
3. Obsidian is mostly made of glass. It is formed by very rapid cooling of thick lava.
B. Intrusive
1. Granite forms within the earth from cooling magma.  Pink granite forms deep within the earth while White granite forms closer to volcanoes. Granite sometimes has glittery specks because of the mineral muscovite. 2. Gabbro forms in the crust where molten mantle has intruded into other rocks.
II. Sedimentary
Sort into clastic and organic.
A. Clastic
1. Conglomerate is a large grained rock that forms from the accumulation of many particles.
2. Sandstone is a medium grained rock that forms from the compression of sand. It is very soft and you can rub the sand off.
3. Shale is a fine-grained rock that forms from mud that is compressed. Sometimes you can see layers in this rock.
B. Organic
1. Coal is the remains of plants and animals that have been compressed over time. Distinctive black color. The dust from digging coal has caused Black Lung Disease among coal miners.
2. Limestone is formed in marine conditions. You can often see fossils in this rock.
III. Metamorphic
Sort these into foliated and non-foliated.
A. Foliated
1. Gneiss (pronounced NICE) forms very deep in the earthÕs crust. It is a high grade metamorphic rock, which means it, forms from a lot of heat and pressure. Gneiss has a very pronounced foliation.
Find the sedimentary rock Shale and compare it to the next three.
2. Slate forms from mud rocks (which kind of sedimentary rock?). It is a low-grade metamorphic rock, which means it metamorphosed at low temperatures and low pressures. You can often see layers in this rock and it is fine grained because it forms form very fine-grained mudstone, so you donÕt see crystals. This rock was the first blackboard used in a school. Pioneer students had to bring a slate to school.
3. Phyllite also forms from mudstones at medium temperatures and pressures. Layers are visible and may have small, distinct crystals visible. They often have a pale grayish green coloring.
4. Schist is also formed from mud and clay based rocks that have undergone medium to high metamorphism (medium to high temperatures and pressures). The presence of the mineral mica gives it a sparkly look and foliation gives it a layered look.
B. Non-foliated
1. Marble is a coarse grained rock that contains visible crystals of calcite. It is made from the metamorphism of limestone. Sometimes it happens when there is an intrusion of igneous rocks and the limestone around it has been heated and recrystallized. Find the sedimentary rock limestone and compare it to marble.
2. Quartzite (also called Metaquartzite) is made from sandstone. It forms because of large igneous intrusions that happen near sandstone. The sandstone heats up and the crystals of the mineral quartz fuse. The pores or spaces between the sand crystals have been squeezed out and a very tough rock is formed.