Properties and the Three Types of Rocks

Minerals  Geologist- A scientist that studies the properties of rocks to tell how they may have formed.  Mineral- A naturally occurring substance that is not a plant or animal  Rocks are made of at least one type of mineral, sometimes many. Minerals are the building blocks of all rocks.  Geologist study different properties of minerals in order to identify and classify rocks.

Properties of Minerals  Color- This is not always useful because many rocks are the same color.  Texture- the way the rock feels. This property helps, BUT many rocks have the same textures and feel the same. Texture examples: rough, smooth, gritty, coarse

 Luster-The way a mineral reflects light. EX: Shiny, metallic, glassy, greasy, dull.  Streak- The line left when a mineral is rubbed on a piece of unglazed tile. For example, gold leaves a gold streak, but pyrite (fool’s gold) leaves a black streak. Diamonds have a glassy luster. Galena has a metallic luster.

 Hardness- The ability of one mineral to scratch another. Can be tested with a fingernail, penny, or an iron nail. For example, talc is the softest mineral. Diamond is the hardest. Mohs’ Scale- A rating that indicates a mineral’s hardness. Talc is the softest. Diamonds are a 10 on Mohs’ Scale. This means they can scratch any other rock.

 Another property is how a rock breaks. Most break into chunks, but some break into flat sheets. This property is called cleavage.  A last property is density. Density- how much something weighs compared to how much space it takes up Think of a golf ball and a ping-pong ball: same size, but totally different weights. A golf ball is more dense. Mica looks like a normal rock, but it breaks into flat, foil-like sheets.

3 Types of Rocks 1. Igneous (“Ring of Fire”) 2. Sedimentary (“Come Together”) 3. Metamorphic (“Changes”)

Igneous Rocks- “fire-made” rock formed from melted rock material.  Magma- melted rock beneath the Earth’s surface.  Lava- magma that reaches the Earth’s surface.

Ring of Fire 1. Igneous Rock- “fire-made” rock formed from melted rock material.  Can form under the ground (magma cools) or above ground (volcano erupts, lava cools)  If the lava cools slowly, the rock feels more rough or coarse. (Under ground)  If it cools fast, the rock feels smoother. (Above ground) Obsidian formed when lava cooled down fast above Earth’s surface. Granite formed when magma under the ground cooled slowly.

Come Together 2. Sedimentary Rocks- Rock formed from bits or layers of rocks cemented together.  Sediment- Deposited rock particles and other materials that settle in a liquid. These sediments will be pushed together over time to form new rock like this sandstone.

Coming Together  Weathering- The wearing away of rock. This process turns any type of rock into sediment.  Cementation- Process that causes sediments to stick together.  Compaction- Process that presses sediments together.  These two processes turn sediments into sedimentary rock.

More Sedimentary Rocks  Relative Age- the age of something compared to the age of another thing.  The sediments of a sedimentary rock are all different ages.  Fossils are found in sedimentary rocks. The oldest layers are at the bottom. The farther down, the older because the new layers pile on top.

Ch, Ch, Ch, Ch, Changes 3. Metamorphic Rock- a rock whose form has been changed by heat and pressure. + heat and = pressure Limestone Marble HINT: Metamorphosis means change in form, so Metamorphic rocks have been changed by heat and pressure.

Ch, Ch, Ch, Ch, Changes  The heat comes from the Earth’s core (which is all magma)  The pressure comes from all the soil, rocks, and everything else pressing down on the rock!!!  Before the change the rock may have been any kind of rock, even another metamorphic rock.