Chapter 13 Minerals of The Earth’s Crust

I. What is a Mineral?

-a naturally formed, inorganic solid that has a definite crystalline structure.

Mineral Structure

To be a mineral, a substance must • be a solid • be inorganic • have a repeating inner “crystalline” structure • be formed in nature

Atoms & Compounds

Minerals are made up of

Elements atoms

are pure substances made of only one kind of by ordinary means.

An

atom

is the smallest part of an element that has all the properties of that element.

Atoms & Compounds cont.

Compounds

are substances made of 2 or more elements that have been chemically combined. Example:

NaCl (salt) Na

is a compound made of (sodium), a metal, and

Cl

(chlorine), a gas. Most minerals are made of compounds but some are composed of just one element and are called

native elements .

Crystals

Solid, geometric forms of minerals produced by a repeating pattern of atoms or molecules that is present throughout the mineral are called

crystals

. Each crystal has a definite shape determined by the arrangement of atoms or molecules within the crystal, and each mineral has a definite crystalline structure. Minerals can be grouped into classes according to the crystals they form.

Silicate Minerals

Minerals are divided into 2 groups based on their chemical composition:

Silicate minerals

-minerals that contain a combination of silicon and oxygen, Earth’s 2 than 90% of the Earth’s crust.

Examples

: quartz, feldspar, and mica quartz feldspar mica

Nonsilicate Minerals

are minerals that combination of the elements silicon and oxygen.

do not

contain a Some are made up of elements such as carbon, oxygen, fluorine and sulfur.

Examples:

copper, calcite, fluorite, corundum, gypsum, galena and others.

galena copper calcite fluorite corundum gypsum

II. Mineral Identification

Color

The same mineral can come in a variety of

colors

, depending on what impurities present and exposure to air long periods of time.

Color is and

not

water are for the best way to identify a mineral.

-is the way a surface reflects light

-

Example

: is something shiny or dull

metallic

-bright, reflective

submetallic

-dull, metallic or nonmetallic

nonmetallic -

6 different descriptions

Luster

Streak

-

Streak

is the color of a mineral in powdered form It can be found by rubbing the mineral against a piece of unglazed porcelain called a “streak plate” The color of a

mineral’s streak

is not always the color of the mineral sample, and is not affected by air or water.

Streak

more reliable for identification is than color.

Cleavage and Fracture

The way a mineral breaks is

Cleavage

is the tendency of surfaces.

Fracture

is the tendency of unevenly along

curved or irregular surfaces.

Hardness

This is a mineral’s resistance to being scratched. Scientists use the

Mohs Hardness Scale

shown below.

Talc

has a rating of

1

and

diamond

has a rating of

10. If the reference mineral scratches your mineral, then the reference mineral is harder than your mineral.

MOHS HARDNESS SCALE

space. It is a

Density

This is the measure of the amount of matter in a given amount of

ratio of an object’s mass to it’s volume.

Water has a density of 1 g/cm³ and so is used as a reference point for other substances. The ratio of an object’s density to the density of water is called its

specific gravity

.

Gold

has a specific gravity of

19

and so contains 19 times as much matter as 1 cm³of water contains.

Pyrite

(fool’s gold) has a specific gravity of

5. Specific gravity can be used to distinguish between gold and “fool’s gold”.

specific gravity ~ how heavy something feels when compared to what you would expect, heft, weight, mass, density

Gold

on chunk of

pyrite

-”fool’s gold”

Special Properties

The following special properties help identify a few types of minerals:

Fluorescence -calcite and fluorite glow under UV light Magnetism -magnetite and pyrrhotite are natural magnets that attract iron Chemical reaction place on it -calcite will become bubbly or “fizz” when a drop of weak acid is Taste -Halite has a salty taste Optical Properties -Calcite will cause a double image when placed over an image.

Radioactivity counter -Minerals that contain radium or uranium can be detected by a geiger

III. The Formation, Mining and Use of Minerals

Minerals form in a variety of environments in the Earth’s crust with different physical and chemical conditions which determine the mineral properties.

Surface Mining

When mineral deposits are located at or near the surface of the Earth, surface-mining methods are used to remove the minerals.

Mineral deposits called ores are mined for profit through surface or subsurface mining.

The method miners choose depends on how close to the surface or how far down in the Earth the mineral is located.

Open-Pit Mining

•is used to remove large, near-surface deposits of economically important minerals such as gold and copper.

•is mined downward, layer by layer •explosives are used to break up the ore •ore is loaded into trucks and taken away for processing

Open-Pit Mining

Trucks the size of houses dump 200-ton loads of waste rock, remnants of mineral mining from an open pit mine in Nevada.

Quarries

Are open pits used to mine building stone, crushed rock, sand and gravel

Strip Mining

Surface mining of coal is done in strips that may be 50m wide and 1 km long

Subsurface Mining cont.

Subsurface Mining

This method is used when mineral deposits are too deep within the Earth to be surface mined.

Subsurface Mining continued

Subsurface mining often requires that passageways be dug into the Earth to reach ore. These passageways may be dug horizontally or at an angle.

Subsurface Mining continued…

Sinkholes can result!

Wall of coal-mining pit near Haybro, Colorado

Responsible Mining

Mining can destroy or disturb the habitats of plants and animals. The waste products from a a mine may get into water sources, which pollutes surface water and groundwater.

Mine Reclamation When land used for mining is returned to its original state or better, it is called reclamation.

During Mining After Reclamation

The Use of Minerals

1 Common Uses of Minerals Mineral

Copper

Uses

electrical wire, plumbing, coins Diamond Galena Gibbsite jewelry, cutting tools, drill bits batteries, ammunition cans, foil, appliances, utensils Gold Gypsum Halite Quartz Silver Sphalerite jewelry, computers, spacecraft, dentistry wallboards, plaster, cement nutrition, highway de-icer, water softener glass, computer chips photography, electronics products, jewelry jet aircraft, spacecraft, paints

Uses of Minerals

Metallic Minerals

have shiny surfaces good conductors of heat and electricity can be processed into metals that are strong and do not rust other metals can be pounded or pressed into various shapes metallic minerals that have many industrial uses are gold, silver, and copper.