Minerals and rOCKS Chapter 2

Words to Know – Chapter 2 Mineral rock-forming mineral erosion Inorganic granite deposition Crystal basalt compaction Streak grain cementation Luster texture clastic rock Mohs hardness scale igneous rock organic rock Cleavage sedimentary rock chemical rock Fracture metamorphic rock foliated Geode extrusive rock rock cycle Crystallization intrusive rock Solution sediment Vein weathering

Lesson 1 – properties if minerals

Properties of minerals A mineral is a naturally occurring solid that can form by inorganic processes and that has a crystal structure and a definite chemical composition. Naturally occurring – all minerals are substances that formed by natural processes. Ex: coal forms naturally from remains of plants that are squeezed tightly together. Solid – A mineral is ALWAYS a SOLID, with a definite shape and volume. Crystal Structure – The particles of a mineral line up in a pattern that repeats over and over again. This repeating pattern forms a crystal. Forms by Inorganic Processes – All minerals must be able to form by inorganic processes. That is, every mineral must be able to form from materials that were not a part of living things. Definite Chemical Composition – A mineral has a definite chemical composition. This means that a mineral always contains certain elements in definite proportions.

Minerals, Compounds and elements Almost all minerals are compounds. In a compound, two ore more elements are combined so that the elements no longer have distinct properties? Different minerals have a different combination of elements. EX: a crystal of quartz has one atom of silicon for every 2 atoms of oxygen. Some elements occur in nature in a pure form, and not as part of a compound. Elements such as copper, silver, and gold are also minerals. Almost all pure, solid elements are metals.

How are minerals identified? Geologists have identified more than 4,000 minerals Each mineral has characteristic properties that can be used to identify it. Color, Streak, Luster, hardness, density, crystal structure, cleavage and fracture.

How minerals are identified Color – only a few minerals have their own characteristic color Streak – the color of the powder from the mineral. The streak color and the mineral color are often different. Luster – term used to describe how light is reflected from a minerals surface.

Hardness Hardness – One of the most useful clues to a minerals identity. The Mohs Hardness Scale is used to rank the hardness of a mineral on a scale from 1-10 This can be determined by a scratch test. A mineral can scratch any other mineral softer than itself; but can be scratched by a mineral that is harder.

Density Each mineral has a characteristic density. Density is the mass in a given space, or mass per unit volume. No matter how large or small the mineral sample is, the density of the mineral always remains the same. To measure density, geologists use a balance to first determine the precise mass of a mineral sample. Then they place the mineral in water to determine how much of water the sample displaces. The amount of water that is displaced equals the volume of the sample.

Displacement https://www.youtube.com/watch?v=GnBQ6vIutDM

Crystal structure The atoms that make up a mineral line up in a regular pattern. This pattern repeats over and over. The repeating pattern of a mineral’s atom forms a minerals crystal structure. Geologists classify crystals by the number of faces, or sides on the crystal. They also measure the angles at which the faces meet.

Cleavage and fracture A mineral that splits easily along flat surfaces has the property called cleavage. Whether a mineral has cleavage depends on how the atoms in its crystals are arranged. Most minerals do not split apart evenly. Instead, they have a characteristic type of fracture. Fracture describes how a mineral looks when it breaks apart in an irregular way.

How do minerals form? In general, minerals can form in three ways. Some minerals form from organic processes. Other minerals can crystallize from materials dissolved in solutions. Finally, many minerals crystallize as magma and lava cool

Organic minerals & Minerals from solutions Some minerals can also form by organic processes. EX: Ocean animals such as clams and corals produce shells and skeletons made out of the mineral calcite. Sometimes the elements and compounds that form minerals can be dissolved in water to form solutions. When elements and compounds that are dissolved in water leave a solution, crystallization occurs.

Minerals from magma and lava Minerals form as hot magma cools inside the crust, or as lava hardens on the surface. When these liquids cool to a solid state, they form crystals. The size of the crystal depends on the rate at which the magma cools, the amount of gas the magma contains and the chemical composition of the magma.

Where mineral resources are found Earth’s crust is made up mostly of the common rock-forming minerals combined in various types of rock. Less common minerals are not found evenly throughout the crust. Instead several processes can concentrate these minerals, or bring them together, in deposits. An ore is a deposit of valuable minerals contained in rocks.