Minerals Mrs. Christopherson 2011

Properties of Minerals What is a mineral? –Naturally occurring –Inorganic –Solid –Crystal structure –Definite chemical composition

Where are minerals found?

Naturally Occurring A naturally occurring substance is one that occurs in the natural world Materials made by people are NOT minerals Would a cubic zirconia be considered a mineral?

Inorganic Minerals cannot form from materials that were once part of living things For example: Coal –What is coal formed from? –Is it considered a mineral? –Would a bone be considered a mineral?

Solid Minerals are solids What are the particles of a solid like compared to those of a liquid or gas? A solid has a definite volume and shape

Crystal Structure Minerals have a crystal structure Crystals have flat sides, called faces, that meet at sharp edges and corners The particles of minerals line up in a pattern that repeats over and over again How does this repeating pattern affect the shape of the mineral?

Crystal Structure

Definite Chemical Composition A mineral always contains certain elements in definite proportions Almost all minerals are compounds What is a compound? Some minerals occur in their pure form –Copper, silver, gold These minerals would also be considered what?

Chemical Composition

Identifying Minerals Geologists have identified about 3,800 minerals Each mineral has characteristic properties that can be observed simply by looking at the sample Other properties must be tested

Identifying Minerals Color An easily observed characteristic Color alone is often too little information to identify a mineral

Identifying Minerals Streak The color of a mineral’s powder Streak and color are often different Streak test= rubbing a mineral on an unglazed ceramic tile

Identifying Minerals Luster Term used to describe how light is reflected from a mineral’s surface –Metallic, glass, waxy, greasy, pearly, submetallic or dull, silky, and earthy MetallicGlassyEarthy

Identifying Minerals Density Each mineral has a characteristic density Density is the mass in a given space –Mass per unit volume

Identifying Minerals Hardness Determined using Moh’s Hardness Scale Determined by scratch test

Identifying Minerals Crystal Systems Crystals of each mineral grows atom by atom to form that mineral’s particular crystal structure Geologists classify these structures into six groups Sometimes the crystal structure is obvious from the mineral’s appearance Sometimes the crystal structure is only visible under a microscope A few minerals are still considered minerals even though their particles are not arranged in a crystal structure

Identifying Minerals Cleavage A mineral that splits easily along a flat surface is said to have cleavage

Identifying Minerals Fracture Most minerals do not split evenly Minerals that break apart in an irregular way are described in terms of fracture –Types of Fracture: Curved, shell-like surface, hackly fracture – rough, irregular surfaces

Identifying Minerals Special Properties Fluorescence, reactivity, magnetism, optical, and electrical

How Minerals Form What is a geode? –A geode is a rounded, hollow rock that is often lined with mineral crystals.

How Minerals Form How does a geode form? –Crystals form inside a geode when water containing dissolved minerals seeps into a crack or hollow in a rock. Slowly, crystallization occurs.

How Minerals Form What is crystallization? –Crystallization is the process by which atoms are arranged to form a material with a crystal structure.

How Minerals Form Two ways minerals can form: –Crystallization of magma and lava –Crystallization of materials dissolved in water

How Minerals Form 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.

How Minerals Form Size – the size of the crystals depends on several factors: – the rate at which the magma cools – the amount of gas the magma contains – and the chemical composition of the magma.

How Minerals Form Size of Crystals: –Rate of cooling: magma that cools below the surface cools slowly over many thousands of years Slow cooling leads to the formation of large crystals.

Size of Crystals: –Rate of cooling: Magma closer to the surface cools much faster – rapid cooling does not provide enough time for crystals to grow large – If magma erupts to the surface and becomes lava it will cool quickly and form small crystals.

How Minerals Form Size of Crystals: –Undisturbed: if the crystals remain undisturbed while cooling they grow by adding atoms according to a regular pattern.

How Minerals Form Minerals from Solutions: –Sometimes the elements and compounds that form minerals can be dissolved in water to form a solution. Solution: a mixture in which one substance is dissolved in another. Solute:

How Minerals Form Minerals from Solutions: –When elements and compounds that are dissolved in water leave a solution, crystallization occurs.

How Minerals Form Minerals formed by Evaporation: –as water evaporates from a solution, crystals form (halite, gypsum, calcite)

How Minerals Form Minerals from Hot Water Solutions: – When magma heats water deep under ground, sometimes elements and compounds that form a mineral are dissolved in it. As the water cools, the elements and compounds leave the solution and crystallize as minerals.

How Minerals Form Vein: –pure metals that crystallize from hot water solutions underground often form veins, or narrow channels or slabs of a mineral that is often different from the surrounding rock. The solutions of hot water and metals often flow through cracks within rocks, allowing the metal to crystallize into a vein.