MINERALS• The building blocks of rocks…..

• Did any of you use minerals before coming to school this morning??? I sure hope so!!

All of these items used to build a house are made of

minerals!

How Minerals Affect Your Life

The Average American will use - • 30,415 pounds of salt• 1.7 million pounds of stone, sand and gravel• 42,581 pounds of iron ore• 1,078 pounds of lead• 27,000 pounds of clay

**Total – 3.75 million pounds of minerals, metals and fuels in your lifetime!!

MINERALS

= a naturally occurring, inorganic solid with a definite chemical composition and a particular

crystalline structure(orderly arrangement of atoms)

1) Naturally occurring

Formed in processes on or in the earth with no human

input

2) Inorganic• Not made by living process*It has never been alive!

Amber (fossilized tree resin) and sugar are not minerals because they formed from living things.

3) Definite chemical composition

• All minerals are elements or compounds with definite chemical composition

ex: mineral halite (NaCl) has a distinctive salty taste

-Copper (Cu) - Beryl (Be3Al2Si6O18)

4) Crystal Structure

• The atoms of the mineral are arranged in patterns that repeat over and over again.

ex) Graphite versus Diamond

Uses of Minerals….Ores - used for metals, extracted by

mining (ex. iron)Gems – rare and beautiful, often

used for jewelry

How to Identify Rocks and Minerals

• The first thing to have when identifying minerals is a good field guide, which you will be able to use compare the physical properties of a mineral to descriptions and pictures in your guide.

• A mineral is any naturally-occurring, homogeneous solid that has a definite chemical composition and a distinctive internal crystal structure. Minerals are usually formed by inorganic processes, but a few synthetic equivalents of some minerals, such as emeralds and diamonds, are often produced in the laboratory for experimental or commercial purposes.

• naturally-occurring

• homogeneous (uniform throughout) solid

• have a particular chemical makeup

• distinctive crystal structure or orderly arrangement of atoms

• usually formed by inorganic processes

Notes on

What is a rock?

• Minerals combine with each other to form rocks.

granite

Properties Used to Identify Rocks and Minerals

• Color• Streak• Transparency• Luster• Hardness• Cleavage• Fracture• Specific Gravity• Crystal Form

CAUTION!    Do not test good mineral samples or anything of value such as jewelry. The damage may be

permanent.

Color• A few minerals

are easily identified by color because they are never any other color. For example, malachite is always green.

                                  

      

Color by itself isn’t enough to identify a mineral.

• Chemical impurities can change the color of a mineral without changing its basic make-up.

• Quartz in its purest form is colorless and clear as glass.

• Quartz with traces of iron becomes violet (amethyst).

• Quartz with traces of manganese turns pink (rose quartz).

• If quartz is exposed to radiation, it turns brown (smoky quartz)..

                                             

                                             

Moh’s Scale of Relative Hardness

Mohs’ hardness scale places ten common minerals on a scale from one to ten.

*one is the softest mineral

*ten is the hardest

Scratch the rock or mineral to determine its hardness

Try to scratch the surface of an unknown sample with a mineral or substance from the hardness scale (these are known samples). If the unknown sample cannot be scratched by feldspar (6) but it can be scratched by quartz (7), then it's hardness is between 6 and 7. If you don't have minerals from the hardness scale on hand, here are some common objects and their hardness values:

fingernail 2.5 penny 3.0 steel blade 5.5

Moh's Hardness Scale:Hardnes

sMineral Scratched by . . . .

1 talc soft pencil lead

2 gypsum fingernail; blackboard chalk

3 calcite copper penny

4 fluorite iron nail; brass

5 apatite steel knife blade

6 feldspar window glass; steel file

7 quartz flint sandpaper

8 topaz spinel(available in rock shops)

9corundu

m emery sandpaper

10 diamond carborundum sandpaper

Moh’s Scale of Relative Hardness

Diamond

• Diamond is the hardest naturally occurring substance known; it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.

• The hardness, brilliance, and sparkle of diamonds make them unsurpassed as gems. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April.

                                          

Streak is the color of the powder

• When a mineral is rubbed firmly across an unglazed tile of white porcelain (a streak plate), it leaves a line of powder. This is called the streak. The color of the streak is always the same, whether or not the mineral has impurities. For example, quartz leaves a white streak, whether it's violet (amethyst), pink (rose quartz), or brown (smoky quartz).

Streak Color for a Few Common Minerals Black - Graphite

Black - Pryite Black - Magnetite

Black - Chalcopyrite Gray - Galena

Limonite - Yellow-brown Hematite - Red-brown

•

Transparency

• Transparency describes how well light passes through a mineral sample.

• 3 degrees of transparency:

• Transparent• Translucent• Opaque. •The samples of beryl

shown here are nearly transparent.

Transparent

You can see objects through a transparent mineral. Examples:

*celestite*rose quartz*quartz crystals

                           

Translucent

• You can see light, but no objects through a translucent mineral.

• Examples:

quartz

calcite

realgar

Opaque

• You can't see anything through an opaque mineral.

• Example:

gratonite

LusterLuster is the way the surface of a mineral reflects light. Luster should be observed on a cut or freshly broken, untarnished surface.

–

                                                                            

Luster

• There are numerous types of lusters, but for identification purposes it is generally sufficient to distinguish only between metallic and nonmetallic minerals. Look at the images below. Which does your specimen most closely resemble? Metallic minerals have the sheen of a metal, like the frame of your desk. Nonmetallic minerals may appear glassy, meaning they allow light to pass through, dull or even waxy. Keep in mind you are not looking at color, simply the way a mineral specimen reflects room light.

The terms used to describe luster are:

• Metallic -- example: gold • Vitreous (glassy) -- example: quartz • Adamantine (brilliant) -- example: diamond • Resinous (like resin or sap from a tree) --

example: sphalerite • Greasy or waxy -- example: turquoise • Pearly -- example: talc • Silky -- example: asbestos • Dull or earthy -- example: bauxite

Metallic Luster

• Examples:

gold

silver

•

                            

              

                            

              

Vitreous or Glassy Luster

• Vitreous (glassy) – looks like glass

• examples:

elbaitequartz (rose quartz

shown)

tourmaline

Adamantine or Brilliant Luster

• example: diamond

Resinous Luster

• (like resin or sap from a tree) –

• example: sphalerite• sulphur

Greasy or Waxy Luster

• example: turquoise

          

  

Silky Luster

• like silk• example:

ulexite

rosasite

Earthy or Dull Luster

• example:– hematite

Pearly Luster

• example: talc

Cleavage

• When a mineral sample is broken with a hammer, it breaks along planes of weakness that are part of its crystalline structure. These breaks are cleavages.

What is Cleavage? Cleavage is the ability of a mineral to break along

preferred planes.

Cleavage

• In some minerals, bonds between layers of atoms aligned in certain directions are weaker than bonds between different layers. In these cases, breakage occurs along smooth, flat surfaces parallel to those zones of weakness. In some minerals, a single direction of weakness exists, but in others, two, three, four, or as many as six may be present. Where more than one direction of cleavage is present, it is important to determine the angular relation between the resulting cleavage surfaces: are they perpendicular to each other (right angle), or do they meet at an acute or obtuse angle?

Some common forms of cleavage are

• Cubic

• Rhombohedral

• basal.

Cubic cleavages form cubes

• Example: halite

                   

Rhombohedral cleavages form six-sided prisms

• example: calcite

             

 

Basal cleavages occur along a single plane parallel to the base of the

mineral• example: topaz

Cleavage

• Many minerals tend to break along sets of well-defined planes, which are related to the internal arrangement of the atoms. This property is known as cleavage. As the quality of the break decreases, cleavage may be described as good, distinct, and poor or none. Some minerals cleave perfectly in one direction and poorly in others. For example, gypsum cleaves perfectly on one plane and poorly along two others

• GYPSUM

Fracture Not all minerals cleave easily. Some

fracture instead. Unlike cleavages, which are usually clean, flat breaks, fractures can be smoothly curved, irregular, jagged or splintery.

Most Common Types of Fracture

• conchoidal (quartz)

• fibrous or splintery

• hackly (copper)

• uneven or irregular.

• Basal cleavage

Fibrous or Splintery

Hackly or Jagged Fractureexample: copper

Conchoidal Fracture

• smooth and curved

• The sample of malachite shown here has a conchoidal fracture

                        

Uneven or Irregular Fracture

• Uneven or irregular edges just as the name implies.

Basal Cleavage

• Makes a clean break in one direction.

• Readily splits into sheets.

• Example:

mica

Hexagonal prism and pyramid

• quartz forms elongated, six-sided prisms capped with pyramid-like faces;

cubes

• galena and halite occur as cubes;

                      

                       

Isometric or Cubic Crystals

• Isometric crystals are usually shaped like blocks, with similar and symmetrical faces. The crystal has three axes of symmetry, all at right angles to each other, and all of the same length.Example: pyrite

– magnetite

Tetragonal Crystals

• Typically, these crystals are shaped like four-sided prisms and pyramids.

• Example: zircon

Hexagonal Crystals

• These crystals are usually shaped like six-sided prisms (hexagonal prism) and/or pyramids (hexagonal pyramids).

• Example: apatite

Orthorhombic Crystals

• These crystals are short and stubby. Each crystal has three unequal axes, all at right angles to one another.Example: topaz

Monoclinic Crystals

• These crystals are short and stubby with tilted faces at each end.

• Example: gypsum

                   

Triclinic Crystals

• Triclinic crystals are usually flat with sharp edges, but exhibit no right angles. Each crystal has three unequal axes. None are perpendicular to one another.

• Example: andesine

Specific Gravity (sg)

• Specific Gravity (sg)  indicates how many times more the mineral weighs compared to an equal amount of water (SG 1). So if you have a bucket of silver, it would weigh 10 times as much as a bucket of water. That is why we think of metals as being "heavy". They are heavy compared to other things that we are used to picking up. This is also known as the "heft" of an object. gold

What is specific gravity?

Specific gravity is the "heaviness" of a mineral. It is defined as a number that expresses the ratio between the weight of a mineral and the weight of an equal volume of water. Water has a specific gravity of 1.

On what is specific gravity dependent upon?

The specific gravity depends on: 1.the kind of atoms that comprise the mineral 2.how the atoms are packed together

You can easily distinguish minerals that have unusually high or unusually low specific gravities, just by the way they "feel" when you hold a sample in your hand.

How is specific gravity measured?

The steps in measuring the specific gravity are:

•weigh the mineral in air (Wa)

•weigh the mineral in water (Ww)

•use the following equation: Wa/( Wa - Ww )

•the resulting number is the specific gravity

Note that the specific gravity is a ratio, there are no units.

Description SG Mineral examples

very light < 2 borax

light 2 – 3 quartz, calcite, halite, dolomite, ulexite, gypsum, turquoise, talc, muscovite, biotite

heavy 3 – 5 barite, chalcopyrite, fluorite, celestite, apatite, almandine garnet

very heavy 5 – 10

nickel-iron, galena, pyrite, magnetite

extremely heavy

> 10 silver, gold

TOP

                          

                   

How rock is formed?

Minerals in your closet

• Hematite: hinges, handles (steel) Chromite: chrome plating

• Quartz : mirror on door

Minerals in batteries

• Graphite

• Galena

• sphalerite

Minerals in your table lamp

• Brass (an alloy of copper and zinc): base Quartz: bulb

• Wolframite: lamp filament

• Copper: wiring

Minerals in your bed

• Hematite: hinges, handles, mattress springs Chromite: chrome plating

Minerals in your wristwatch

• Hematite: band, frame Chromite: plating

• Quartz: time keeper

• Pentlandite: watch spring