I. Minerals

Definitions – Earth MaterialsA. Rock: naturally occurring aggregate of

one or more mineralsB. Mineral: naturally occurring solid with a

definite chemical composition and an orderly internal structure.

Natural: synthetic gems and other substances created by chemists are not minerals

SolidDefinite chemical composition: consists

of one or more chemical elements in specific proportions

Orderly internal structure: elements are arranged in a systematic way that is the same in every sample of that particular mineral

Minerals

Rocks and Minerals

At one time or another, you have probably held a rock in your hand

Recall the color.

Recall the size.

The word rock refers to solid mineral deposits.

Rocks are minerals, but not all minerals are rocks. Minerals are all substances that can't be classified as "animal" or "vegetable."

                                          

  

                                          

  

Minerals

Metals ores found in the earth, like gold and silver, are minerals.

Crystalline substances, like salt and quartz, are minerals.

Homogeneous natural substances, like water and gas, are also minerals.

These non-solid minerals?"

Rock: an aggregate of one or more minerals

                                          

  

                                          

  

Minerals

(a) atomic structure and chemical reactions: a review

(b) What is a mineral?

(c) Classification of minerals

(d) Silicate minerals

                                         

         

What is a mineral?

First we need to understand atomic structure of elements.

Atomic structure and chemical reactions

STRUCTURE OF ATOMS: Atom is the smallest unit of an element that retains the physical and chemical properties of that element.

Atom: the smallest particles of an element that retain all of the element’s chemical properties

Chemical Compounds: specific combinations of one or more elements.Atoms bond together to form compounds

a. SiO2, NaCl, PbS, Fe2SiO4, CaAl2Si2O8

All of the above are chemical formulas of minerals

b. Minerals are essentially chemical compounds; elements, in certain proportions, bonded together

A. Relative abundances of elements

Of the 92 naturally occurring elements, 8 make up >98% of the Earth’s continental crust

Most minerals in the crust are O and Si based rocks (silicates)

Most minerals in the mantle are O-Si-Fe-Mg based rocks

Composition of Earth Crust Entire Earth

1. Oxygen (O) 45.2% 29.3% (2)2. Silicon (Si) 27.2% 14.7% (3)3. Aluminum (Al) 8.0 1.2% (8)4. Iron (Fe) 5.8% 34.8% (1)5. Calcium (Ca) 5.1% 1.4% (7)6. Magnesium (Mg) 2.8% 11.3% (4)7. Sodium (Na) 2.3%8. Potassium (K) 1.7% Sulfur (S) 3.3% (5) Nickel (Ni) 2.4% (6)

Total 98.1% 98.4%

CHEMICAL REACTIONS and TYPES OF CHEMICAL BONDS

Ions = atoms that gained and lost electrons:

Ions -- after gain or loss of an electron, atoms are no longer electrically neutral.

When Na loses an electron it becomes a Na ion.

Positive ions = cations,

Negative ions = anions.

CHEMICAL REACTIONS

TYPES OF CHEMICAL BONDS

Relative sizes and charges of these elements’ atoms and ions

1. Given two elements of equal abundance, the element that will contribute more readily in a mineral is the one that “fits” better with the other elements.

2. Ions pack together as closely as possible (large negative ions with small positive ions in the “holes”.

3. If amount of one element runs low, it may be replaced by another.

TYPES OF CHEMICAL BONDS

One type of atomic bond is:

Ionic substitution: ions of similar size and shape (charge) replace one another within a crystal structure

For example Mg and Fe2+ in olivine: (Fe, Mg)2SiO4 )

Na (+1) and Cl (-1), + and – attract, so Na loses an electron and Cl gains an electron

Ionic substitution

Ions of similar size and shape (charge) replace one another within a crystal structure

Ca and Mg can substitute each other

O and Ca can not replace another

The temperature and pressure at the time of formation (Structural Variation)

Polymorphs: minerals with the same composition, but different structures because they formed under different conditions of heat and pressure

For example, diamond and graphite are both pure carbon, one very hard & one soft.

Diamond needs high pressure (>90 miles)Graphite more stable at Earth’s surface

III. Identifying Minerals

Identifying minerals is the key to geology.

We ID the minerals to know what rock it is and where it came from.

The minerals tell us a story about where the rock formed and under what conditions

A. Color: first thing you notice, but least reliable, can vary greatly (quartz, calcite, salt)Color depends on the composition and structure.

Corundum = clear Chromium = red rubies Titanium & Iron = blue sapphiresLithium = pinkCopper = green

                                 

III. Identifying Minerals

B. Luster; how its surface reflects light-- its shininess

MetallicSilkyVitreous (glassy)Earthy (dull)

C. Streak—the color of a mineral in its powered form.

Scrape the mineral across an unglazed porcelain tile (streak plate)

Different color powder than how the mineral looks alone

III. Identifying Minerals

D. Hardness: how hard it is - resistance to scratching or abrasion

Scale from 1-10

Diamond 10Steel 6.5Glass 5-6Copper penny 3.5Fingernail 2.5Graphite 1-2

E. Smell and TasteSulfur- rotten eggsHalite- salty Sylvite- bitter

F. EffervescenceRocks containing CO3 react with HCl to

form CO2 gas                                  

III. Identifying Minerals

F. How they break

1. Cleavage: tendency to break consistently along distinct planes in the crystal structure due to weak bonds---break along flat surfaces called cleavage planes1. cubic—halite 2. sheets—micas 3. rhombus—calcite

2. Fracture—breaks are jagged and irregular

conchoidal fracture: breaks like glass -curved, shell shaped surface

Int-A.02b

Dr. Kent Ratajeski, Department of Geology and Geophysics, University of Wisconsin,

Madison

Analytical techniques

X-Ray Diffraction

Nobel Prize for determining the structure of halite (salt)

Microprobe

Ion Probe