Minerals

Review of Elements

An element is a substance that can not be broken down into other substances.

113 known elements (92 occur naturally)

Periodic table of the elements Examples – Oxygen, hydrogen, gold…

Review of an Atom

An atom is the smallest possible particle of an element that still has all the properties.

Review: Parts of an Atom

Electrons - (negative charge) Orbit around the nucleus in energy levels or shells

Protons - (positive charge) Located in nucleus

Neutrons – (neutral charge) Located in nucleus

Atomic Number

Atomic number – represents the number of protons in an atom.

Neutral atoms have the same number of protons (+ charge) and electrons (- charge)

The atomic number is used to organize elements in the periodic table

Examples of Atomic #, Atomic Mass Number

Atomic Mass and Isotopes Atomic mass – Total number of

protons and neutrons (in nucleus)

Number of neutrons in an atom can change without affecting the atom. Elements containing different numbers of neutrons are called isotopes

ex) Carbon 12 vs. Carbon14

Forming Minerals

Some minerals can form from one element only.

Example. Gold (Au) Most minerals form when they one or

more elements combine together. Example quartz (SiO2)

How do elements bond together?

Elements bond together by sharing their electrons known as covalent bonding

Electrons are given or taken away from one element to another ionic bonding

The Chemistry behind Table Salt

Chemical formula is NaCl Composed of Sodium (Na) and

Chloride (Cl) Alone, sodium is soft, shiny,

potentially explosive Alone, chloride can be a toxic gas Together they form harmless and

essential table salt

Most common minerals Of the 92 naturally occurring elements, only

8 make up 98% of the Earth’s crust Two very important elements

oxygen and silicon. They combine covalently to form a 4-sided

pyramid (known as a: tetrahedron)

Minerals containing silicon-oxygen tetrahedron are called silicates (make up 1/3 of the minerals on Earth)

Definition of a mineral

A naturally occurring solid that is crystalline (repeating arrangement of atoms) and has a specific chemical composition (chemical formula).

Quartz crystals with Hematite "rosettes”

http://www.exceptionalminerals.com/tucson2011-4.htm

Orange Zircon

Tourmaline “watermelon”

More about minerals…

Minerals are the building blocks of rocks.

4000 minerals have been identified A mineral must:

Occur naturally Have a chemical composition (formula) Contain crystals (chrystalline)

Mineraloids:

A mineral that does not have all three defining characteristics.

Example: Opal, Chrysocolla

How do geologists identify minerals?

To identify an unknown mineral, you should:

first determine its physical properties,

then match the properties with the appropriate mineral, using a mineral identification key.

Physical Properties of Minerals To identify a mineral, geologists will study

various physical properties:1. Colour2. Streak3. Lustre4. Hardness5. External crystal form6. Cleavage7. Fracture8. Specific gravity9. Other: Chemical tests

1) Color not always reliable

because color can be changed by the presence of impurities within the mineral, by the type of light used (natural, artificial), by weathering of the mineral’s surface.

Azurite is always blue, malachite is always green.

2) Streak Color that is displayed when the mineral is

rubbed across a streak plate (more reliable than just external color).

Streak color will not always be the same as the color of the mineral.

Galena streaks gray;Hematite streaks red.

3) Luster

how the mineral’s surface reflects light (shiny, glassy, silky, pearly, etc.)

Galena has a metallic luster

4) Hardness

The “scratchability” or hardness of a mineral.

For a true hardness test, the hardner mineral or substance must be able to make a groove or scratch on a smooth, fresh surface of a softer mineral.

Example…

Example of hardness test: Quartz

Quartz can always scratch calcite

Mohs’ hardness Scale

10 minerals are designated as standards of hardness. Softest mineral = talc Hardness mineral = diamond http://www.youtube.com/watch?v=7piTh

8mH9zw

Mineral HardnessHardness of Some Common Objects

Talc 1 

Gypsum 2 

   Human fingernail (2.5)

Calcite 3 

   Copper penny (3.5)

Fluorite 4 

Apatite 5 

   Glass (5-6)

   Pocketknife blade (5-6)

Orthoclase (potassium feldspar) 6 

  

Steel file (6.5)

Quartz 7 

Topaz 8 

Corundum 9 

Diamond 10 

Mohs Hardness ScaleIn

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Hardness Test… Geologists rely on common objects to

test for hardness. Fingernail usually has a hardness of

about 2.5 If you can scratch a mineral with your

fingernail it has a hardness of less then 2.5. A penny has a hardness between 3-4 A knife blad or a steel nail generally has

a hardness of slightly greater than 5. Glass has a hardness of ~ 5.

How to conduct a hardness test on a mineral:

Website: http://www.oum.ox.ac.uk/thezone/minerals/detect/hardness.htm

Video Clip http://www.youtube.com/watch?v=Pz0L6LwGswA

Mohs’ Scale Activity

Complete activity sheet

5) Crystal Form

The set of faces that have a definite geometric relationship to one another.

Examples

ZIRCONGYPSUM

RHODONITEQUARTZ

6) Cleavage

tendency to break consistently along distinct planes.

Example, halite always forms cubes

7) Fracture

When minerals don’t cleave, they fracture – break at random, forming jagged, irregular surfaces.

8) Specific Gravity is a comparison of

the weight of the mineral to the weight of an equal volume of water.

Example: GOLD has a specific

gravity of 19.3, which means that it weighs 19.3 times as much as an equal volume of water.

Specific Gravity…

Specific gravity can be used to distinguish gold from pyrite (fools gold) which has a specific gravity of only ~4.

9) Other Tests: Smell and Taste

sulfur-containing minerals stink like rotten eggs

halite is salty tasting

Sulfur Halite