Properties of MineralsProperties of Minerals

What are minerals?What are minerals?

• There are over 3000 minerals.

• Roughly 100 common minerals

• A mineral is a naturally occurring, inorganic solid that has a crystal structure and definite chemical composition.

5 Characteristics of Minerals5 Characteristics of Minerals

• Naturally Occurring

• Inorganic

• Solid

• Crystal Structure

• Definite Chemical Composition

Naturally OccurringNaturally Occurring

• Formed by geological processes not man.

• Ex: Copper is a mineral but steel is not because it is made by man.

InorganicInorganic

• A mineral cannot be made from a material that was once a part of a living organism.

• Ex: Oil and coal form naturally in the Earth’s crust, but form from the remains of animals and plants from millions of years ago.

SolidSolid

• A mineral has to be solid with a definite shape and volume.

• In a solid the molecules are packed tightly so they cannot flow freely, so the object keeps it’s shape.

Crystal StructureCrystal Structure

• A mineral is made up of a pattern that continually repeats

• The repeating pattern of a mineral’s particles forms a solid called a CRYSTAL.

• Sometimes you are able to see the crystal with the naked eye other times you must use a microscope.

• Opal is considered a mineral even though their particles are not arranged in a crystal structure.

Definite Chemical CompositionDefinite Chemical Composition

• A mineral has a definite chemical composition.

• Meaning: Minerals contain certain elements in definite proportions.

• Almost all minerals are compounds: made of 2 or more different elements bonded together.

• Some minerals are made of one element: Examples are gold, silver, and copper.

Element, Compound, MixtureElement, Compound, Mixture

• Mixture: is a substance composed of two or more substances that re mixed together but not chemically.

• Each substance in a mixture keeps their separate properties. Example: Salt Water

• Element: a substance composed of one type of atom. Each element has unique chemical and physical properties.

• Compound: is a substance composed of two or more elements where the elements no longer have distinct properties.

• Each compound has it’s own properties that differ from the properties of each element.

Identifying MineralsIdentifying Minerals

• Gold Rush: COLOR ALONE WILL NOT WORK!

• Each mineral has its own unique physical properties that can be used to identify it.

• The following characteristics can be used to identify minerals:– Hardness Color Streak– Luster Density Crystal Systems– Cleavage/Fracture Special Properties

ColorColor• Very simply what is the color of the

mineral.

• This can be easily seen however color can only be used to identify a few minerals because only a few minerals have their own characteristic color.

• For example azurite is always blue.• Some minerals like quartz are found in

several colors.

StreakStreak• The streak of a mineral is the color of its powder.

• You can determine this by rubbing a mineral against a piece of unglazed tile called a streak plate.

• The color of a mineral may vary, but its streak will not.

– Pyrite: Gold color Greenish black streak– Gold: Gold color Yellow streak

LusterLuster• This term is used to describe how a mineral reflects

light from its surface.

• Minerals containing metals are often shiny.

• Ex: Galena: Metallic Luster

• Some of the terms used to describe a non-metallic luster in minerals:– Glassy, earthy, waxy, pearly, silky.

HardnessHardness

• How hard a mineral is an excellent tool for identifying the mineral.

• MOHS HARDNESS SCALE was invented to test and compare the hardness of different minerals.

• The scale ranks 10 minerals from softest to hardest.

Hardness (continued)Hardness (continued)

• A mineral can scratch any mineral softer than itself and it will be scratched by any mineral harder than itself.

Mohs Hardness ScaleMohs Hardness ScaleMohs Mineral Hardness Example Other Mineral  Talc 1   

1.5  GraphiteGypsum 2  “  

2.5 Fingernail “ Calcite 3 Copper coin     Fluorite 4      Apatite 5 Steel nail  

5.5 Glass plate  Orthoclase 6   

6.5 Steel file Quartz 7  Garnet   Topaz 8      Corundum 9      Diamond 10  

DensityDensity

• Each mineral has a characteristic Density.

• Density = Mass / Volume (remember the heart)

Crystal SystemsCrystal Systems

• Crystals of each mineral grow atom by atom to form that mineral’s particular crystal structure.

• There are 6 groups/ mineral structures:• Cubic Hexagonal Tetragonal • Monoclinic Triclinic Orthorhombic

CleavageCleavage

• A mineral that splits easily along flat surfaces has this property.

• Cleavage is determined by the arrangement of atoms inside the mineral.

• Depending on the arrangement minerals may split more easily in one direction than another.

FractureFracture

• Fracture describes how a mineral looks when it breaks apart in an irregular way.

Special PropertiesSpecial Properties• Some minerals have special properties

such as FLUORESCENCE.

• These minerals will glow under fluorescent light.

• Some minerals are magnetic. Ex: Lodestone

Special PropertiesSpecial Properties

• Calcite fizzes and gives off Carbon dioxide when you drop acid on it.

• Quartz has electrical properties:– If pressure is applied to these crystals a small

electrical current is produced. Because of these properties, quartz crystals are used in watches, microphones, etc.