Earth Materials & Processes Chapter 1

Minerals

Why Do We Need Minerals?

A Mineral Has 4 Properties

•             Naturally occurring – formed by processes on or inside Earth with no input from humans

•             Inorganic – not made by life processes (ex: decaying animals)

A Mineral Has 4 Properties

•             Has a definite chemical composition – each sample is made of the same elements and compounds

•             Orderly arrangement of atoms

a.    All minerals are crystalline solids

 

Crystal Structure

•      Crystals  are solids with atoms arranged in orderly, repeating patterns

•      Hexagonal

–   Surfaces at 60° or 120° angles

 

•      Cubic

 

Crystal Structure

•      Tetragonal

–   Like cubic, but one direction is longer

 

•      Orthrombic

–   Like cubic, but none of sides   are equal

Crystal Structure

•      Monoclinic

–   One right angle and the rest are oblique

 

•      Triclinic

–   Unequal in all directions and angles

Crystal Formation

•      Some crystals form magma, hot melted rock below Earth’s surface.

–   When magma cools slowly, crystals are large

–   When magma cools quickly, crystals are small

Crystals

•      Crystals can also form from solutions (elements dissolved in water)

–   As the water evaporates or if too much of a substance is dissolved in the water, a crystal forms

 

Composition

•      Mineral groups are defined by their composition (what they are made of)

•      Silicates contain silicon, oxygen, and one or more other elements

–   they include most rock-forming minerals

•      Silicon and oxygen are the two most abundant elements in Earth’s crust

–   They form the building blocks of many materials

Mineral Identification

•      Color and appearance are NOT enough to distinguish most minerals (though they are the most well-known)

•      Hardness is a measure of how easily a mineral can be scratched

–    the Mohs scale compares mineral hardness

–    Slide 14

 

Mineral Identification

•      Luster is the way a mineral reflects light

•      Luster can be metallic

–   Looks like a piece of shiny metal

•      Luster can be nonmetallic

–   Includes dull, pearly, silky and glassy

 

 

Mineral Identification

•      Specific gravity is the ratio of a mineral’s weight of an equal volume of water

–   Expressed as a number

–   Ex:  Gold’s specific gravity is about 17

•    This means that Gold is 17 times heavier than water

–   Ex: Pyrite (fool’s gold) has a specific gravity of 5

•    This means it is 5 times heavier than water

Mineral Identification

•      Streak is the color of a mineral in powdered form

–   This test is only useful for minerals softer than the streak plate

Mineral Identification

•      The way a mineral breaks can be a distinguishing characteristic

•      Minerals with cleavage break along smooth, flat surfaces

•      Minerals with fracture break with uneven, rough, or jagged surfaces

Mineral Identification

•      Some minerals have unique properties

•      Ex: Magnetite is attracted to magnets

•      Ex:  Calcite reacts chemically with hydrochloric acid

Gems

•      Gems are rare and beautiful minerals that are highly prized

•      The Cullinan diamond (biggest ever) and the Hope diamond (has bad luck) are famous historical gems

•      Gems can be used in cutting things (diamonds), to focus lasers, and in electronics (quartz in watches)

 

 

Useful Elements

•      Minerals can be made of useful elements

•      An ore is a mineral or rock containing a substance that can be mined at a profit

–   Ex:  magnetite contains iron

•      Elements can be refined, or purified from ores

–   Ex:  if you refine the mineral bauxite, you can get aluminum

Useful Elements

•      Sometimes, metallic elements dissolve in fluids.

•      They then flow through cracks in rocks and form mineral deposits called vein mineral deposits

–   These deposits can be useful

•      Titanium is derived from the minerals ilmenite and rutile

–   Used for golf clubs, car parts, aircraft, glasses, wheelchairs