Atoms, Elements and Minerals

Start by looking at the structure of the earth.

The earth can be divided into three major parts: the crust, mantle and core

The Crust is the thin outer layer of the earth and there are two types of crust: continent and oceanic.

The crust is composed of rocks (naturally occurring, consisting of material composed of one or more minerals) In other words, a rock is simply an aggregate of different minerals.

A mineral is composed of atoms arranged in a very orderly & 3-d solid structure (a mineral could be defined as the substance that makes up rocks).

What makes a substance a mineral?

A mineral is a naturally occurring inorganic solid with a definite chemical composition and a crystalline structure- they are made up of one or more elements

Elements- the fundamental materials of chemistry that cannot be broken into simpler substances by ordinary chemical process. There are 92 natural occurring elements. Eight of these (oxygen, silicon, aluminum, iron, calcium, magnesium, potassium, and sodium) make up > 98% of the crust. There are 112 elements (Physics Today Sept. 1997 p7).

Elements

The atomic mass number of an element is given by the sum of neutrons and protons in that element.

The atomic weight = number of an element is the weight of an average atom of an element, given its atomic mass unit.

The atomic number of an element is determined by the numbers of protons- this number controls the character of an element more than the other sub atomic particles.

All atoms of an element have same number of protons.

Isotopes- atoms containing different numbers of neutrons but same number of protons.

Elements are in turn composed of atoms

Solids without orderly atomic arrangement are referred to as GLASSY or AMORPHOUS.

Atoms are the fundamental units of elements; i.e. the smallest possible particle of an element that retains the property of the element.

An atom consists of a Nucleus, Electrons, Protons (Nuclei = protons + neutrons)

The chemical behavior of an element depends on the number and orientation of electrons.

Chemical activity

Atoms that are not electrically neutral tend to react with other atoms to neutralize the electrical imbalance.

Some elements become electrically out of balance when their electron shell is complete

Positive (+) or Negatively (-) charged elements are called ions.

Positively charged ions are called Cations and negatively charged ions are called Anions.

Groups of ions may form complex ions, for example, SO₄-2. Chemical formulars show the relative proportion of atoms or ions in compounds

Sketch of sodium ion (Na atomic # 11)

Positive + or Negative - charges are attracted to each other and can be held in place or bonded.

Chemical Bonding

Ionic bonding

Example: sodium chloride (NaCl) is a common mineral.

Covalent- when atoms mutually share their electrons.

Examples: diamond and water.

Metallic- electrons are not held in a particle place but is a pool making metals to be very conductive

Van der Waals- weaker electrical forces result from uneven distribution of electrons

around individual molecules.

Examples: Talc and graphite

Chemical Composition of the Earth's Crust

Oxygen and silicon make the bulk of the Earth's crust as they make up the bulk of the minerals.

Silicon dioxide (SiO₂)- (silicon and quartz)- a type of silicate mineral.

Only 8 elements ( oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium) account for 98% of the weight of the crust.

Five conditions for considering a substance a mineral

Crystalline (solid), natural occurring, inorganic, definite chemical composition, characteristic physical properties.

Crystals/ Crystallinity

A crystal - a substance in which the atoms are arranged in a regular repeating orderly pattern

Silicate tetrahedron

Basic building block SiO₄)4-

Visual learning ... Silicate Structures with animations. Silicate Structures (silica tetrahedron, Single chain, Double chains, Sheet Silicate & framewrk)

Olivine (Mg,Fe)₂ SiO₄

The individual silicon tetrahedrons are bounded together by positively charged ions by Olivine (iron, magnesium) Silicon 4oxygen

Starting with microscopic crystal, the mineral grows through cooling, evaporation, rearrangement of solid materials at high temperature. Grains of initial crystals are grown over.

Factors affecting arrangement of ions/atoms

Number and size of neighboring atoms or ions and size…increases with the number of electrons and electron shells.

Polymorphs. Chemical substances with same exact combination of elements but with different crystalline structure and therefore different mineral

Ask class for definition of a mineral

Most important minerals fall under first five mineral groups

Silicate group (SiO4)₄-

Seven rock forming silicate minerals: olivine, pyroxene, amphibole, mica, clay, feldspar, quartz

3-D network…Feldspar

Single chain Pyroxene (Augite ... two cleavage planes ~90 degrees)

Double chain Amphibole (Hornblende….two cleavage planes-60/120)

Framework Quartz

Sheets -Mica

Carbonate (CO₃)-2 Calcite

Sulfate (SO₄)_-2 Gypsum

Sulfide (S-) Lead Sulfide (Galena)

Oxides (O) hematite, Corundum, Magnetite

Halides (Halite) Sodium Chloride

Phosphates (PO₄) Apatite

Hydroxides (HO)

Organic Coal

Mineraloid

Natives Gold, copper silver

"Common Nonsilicate Mineral Groups

Mineral Group        Example Mineral                     How People Use Them

Oxides                    Hematite (Fe₂O₃)                             Ore of iron
             (Magnetite, another type of oxide)
Sulfides                    Pyrite (FeS₂)                                     Known as fool’s gold
Sulfates                    Gypsum (CaSO₄ (+2H₂O))            Used to make plaster
Halides                    Halite (NaCl)                                    Table salt
Carbonates               Calcite (CaCO₃)                            Used to make cement
Native Elements        Sulfur (S)                                        An ingredient of drugs and chemicals
from http://www.windows.ucar.edu/tour/link=/earth/geology/nonsilicates2.htmlh

Physical Properties of Minerals

Color- not always useful, for example, Quartz has several colors. But at times, color becomes important...Muscovite-white, yellow color for sulfur, green or black or colorless for most ferro magnesium minerals (Augite, hornblende, olivine, biotite)

Streak- crush or pulverized mineral's color for example, Hematite leaving reddish brown streak

Luster- quality & intensity of light reflected from the surface of a mineral. Metallic /nonmetallic Nonmetallic-glassy or vitreous and earthly, luster resinous, silky or pearly

Hardness- is determined by the ease of scratching of the mineral.

Mohs' Hardness Scale

1.Talc

2. Gypsum

Finger nail ~2.5

3. Calcite

Copper Coil ~3.5

4. fluorite

5. apatite

Knife blade and glass ~5.5

6. Orthoclase feldspar

Steel File ~6.5

7. Quartz

8. Topaz

9. Corundum

10. Diamond

Remembering the scale: (The Great Cow Flew And Felt Queer To Come Down)

Crystal form- of a mineral is a set of faces that have a definite geometric relationship to one another (law of constancy of interfacial angles or Steno's law) e.g. calcite, Quartz, Galena.

Cleavage- ability of a mineral to break along a preferred plane. Quartz has no cleavage while mica has one perfect cleavage

Fractures- the way a substance breaks, not controlled by cleavage, for example, quartz has conchoidal fracture.

Specific gravity- heaviness e.g. Galena 7.5 , Quartz 2.65 and Gold 19.3...Specific gravity is a unitless quantity, defined as the ratio of the weight of the substance to the weight of an equal volume of water of 4 degree Celsius.

Gravity µ = m/_v

Specific gravity is G = µ/µ_water

Others- striations (k-feldspar), magnetite, double refraction (calcite) fluorescence mark

Video

A video on plate tectonics "The Earth as a Living Machine"... not available to online class

Molten liquid

Earth's not 6,000 years but it ~ 4.5 Billion years old

Cyclicity of weathering erosion deposition

Wegener..... moving continents.... Pangea - Single landmass Pangea

Dynamic earth

40,000' above the sea floor .. Sea Mount.

No rock is older than 150my (~200my) in the sea

Meaning ~ 95% of the earth's rocks are.....

Henry Hess- proposed sea floor spreading-

Geo-poetry

Lava cooling freezing magnetic directions magnetite theory of floppy Reversed hypothesis Cox flip in 4 m. yr

Vine & Matthews - sea floor spreading established

1968 in S. Atlantic Lomers drilling project.... 1^st confirmation of sea floor spreading