Rock: aggregate of different minerals

Mineral: 

    Naturally occurring

    Inorganic

    Crystalline structure

    Definite chemical properties

    Definite physical properties

Mineraloid: no crystalline internal structure

Composition of minerals

Minerals like all matter are made of elements. (there are more than 100 known elements, some, which we do not know, but already are calculated based on the periodic table).

There are minerals: such as gold, silver, copper, which are composed of only one element. such as gold, silver, copper, which are composed of only one element.

Other minerals: are composed of more than one element joined to form compounds. are composed of more than one element joined to form compounds.

First let’s see what is an atom?

Atom is the smallest component of matter and is still shows the characteristic of that element

 Nucleus of tightly packed protons and neutrons with a surrounding cloud of electrons. In the nucleus the following particles could be found.

        mass of proton is taken as the unit of atomic mass.

    Neutron: electrically neutral it has about the same mass as the       

    proton.

Electron: much smaller than proton or neutron (its mass is approximately 1/1850 of the proton). It carries an electrically negative charge, which has the same strength as the positive proton. Electrons are orbiting very fast around the nucleus. Individual electrons are located at certain distance from the nucleus in regions called energy-level shells, each of them can be hold certain number of electrons.

First shell holds up to two electrons, while every other holds eight or more.

First the lower energy level shells have to be filled up.

The outrermost shell will hold no more than eight electrons.

Mass of an atom: since electron is really small the whole mass of the atom practically equal to the mass of neutrons and protons in the nucleus

Atomic number: number of protons in the atom determine the name of the element.

    for ex. all atoms with six protons called carbon

    atoms with one: hydrogen

    with eight: oxygen

Mass number: the number of protons + the number of neutrons: the number of protons + the number of neutrons

The number of electrons: they have to be the same as the number of protons in neutral atoms, and they exactly balance each other, since neutrons have no electrical charge.

no!!!!!!!!!

    no!!!!!!!!!

    They are neutral, when uncombined!!!!!!

Element: large collection of electrically neutral atoms having the same atomic number

Hydrogen

One proton in the nucleus, one electron surrounding the nucleu

Isotopes: the number of protons in the atoms of a certain elements is constant, however the number of neutrons can vary. They are stable, or instable (emitting atomic particles as radioactive energy)

Bonding

Elements electrically combine with each other to form wide variety of more complex substances, called compounds.

Most of the time the electrons on the outermost shell will be involved in chemical bonding.

Already mentioned, that the outermost shell will hold eight electrons if it is completely filled.

Most of the time it is not filled however, except the noble gases, such as neon, argon (they are the most stable elements).

An atom wants to obtain its lowest energy level, which is the completely filled outermost electron shell (octet rule).

In order to fill the outermost electron shell atoms can loose or gain electrons.

If it happens the atom looses its neutral electric charge, and becomes charged

Valence electron: the electron involved in bonding process. the number of this electrons will determine the number of bonds the element will form.

(Oxygen - 2

Hydrogen - 1

Silicon - 4)

Ionic bonds:

One or more valence electron are transferred from one atom to the other. The atom gaining of loosing electron.

Interesting, how much of the chemical properties are different for the same element as atom, ion, or compound

Covalent bonds:

No electrons are gained or lost, but shared. means that electrons are orbiting two atoms, to acquire the stable noble gas arrangement.

best example:silicates: where the element silicon forming covalent bonds with oxygen

Mixture of the two major bonds are frequent:

    ex. silicates covalent: with oxygen, and Silicon

    ionic: with metallic ions

Metallic bond: with large number of valence electrons moving through the entire aggregate of ions. the given electrons are not bounded to a specific ion pair, but moves about.: with large number of valence electrons moving through the entire aggregate of ions. the given electrons are not bounded to a specific ion pair, but moves about.

A mineral is composed of an ordered array of atoms chemically bonded together to form a particular crystalline structure.

What determines the structure of a crystal??????

- charge of the ion

- size of the ion

(every positive ion will be surrounded by the largest number of Negative ion which will be fit around it) (4,6,8)

- pressure and temperature of formation

Some elements can arrange together in more than one form

(polymorph) calcite, aragonite;

graphite, diamond

Graphite, and diamond has very different crystal structure, because they formed on a very different way.

Diamond 200km deep, high pressure caused very compact struct.

Graphite: loose structure weekly bonded atoms, under smaller pressure

Physical properties of minerals

How did people realize, the internal crystalline structure, to be very characteristic for every mineral??????????

Steno: figured, that independently 1600 from the size of the crystals they all have the same angles between the crystal faces

Hauy(1700):accidently dropped a piece of calcite and observed its cleavage. he than did it to check what happened? he thought that the calcite is composed of thousand of rhombohedron his discovery was very important.

1. Crystal form

If a crystal has space to grow in unrestricted it will develop natural crystal faces and assumes a specific geometric form. The shape of the crystal reflects its inside structure. (if the atoms are arranged in a long chain, the crystal may be needle like; if they arranged in a box like network: they will form cube.

2. Cleavage

2. Cleavage

the tendency of the crystal to split or break along smooth planes paralell to zones of weak bonding in the crystal structure. it can be perfect such as mica where to break in any other direction is hard.

sometime, the weakness is not that great, than the cleavage is poor.

there can be more than one cleavage direction in a crystal, but in a certain mineral it is always the same

(calcite 3 (rhombohedron)

mica 1 (form thin flat seets)

nacl 3 (cube)

If a mineral has no weakness direction in their structure, they will have fracture

quartz -----choncoidal

3. Hardness

hardness is the measure of a mineral’s resistence to abrasion. this is very useful, and easy to do.

Frederick Mohs (~1800)

His scale of 1 to 10 is provide a standard testing a mineral hardness.

4. Specific gravity

Specific gravity is the ratio of the weight of a volume of a substance to yhe weight of an equal volume of water.

ex: 1 kg solid lead is 11 times heavier than 1 kg water. so specific gravity of lead is 11.

The more numerous are the atoms in a mineral, and the more compact, the larger is the specific gravity.

examples.

quartz 2.65

olivine 3.37

You can fill it by picking up the mineral. heavier have larger specific gravity

5. Color

it is one of the most obvious property of a mineral, but often unreliable. slight impurities can give different color.

Exotic coloration -- caused by impurities -- caused by impurities

quartz

calcite

Inherent coloration---

sulfur yellow

malachite- bright green

hematite - red

pyrite - yellow

6. Streak

the color of the mineral in its powdered form. (unglazed porcelan plate streak plate) nonmetallic minerals usually do not have very characteristic streak.

7. Luster

the apparance of light reflected from the surface of the mineral.

Mineral Groups

4000 existing mineral, even today 40 in each year are discovered.

The one’s that are most common in rocks called rock forming minerals.

In rock forming minerals there are about 8 elements, which are the most common elements in the continental crust.

Most common elements in the Earth’s crust:

Oxygen (O) 46.6%

Silicon (Si) 27.7%

Aluminum (Al) 8.1%

Iron (Fe) 5%

Calcium (Ca) 3.6%

Sodium (Na) 2.8%

Potassium (K) 2.6%

Magnesium (Mg) 1.5%

all others 1.5%

The two most abundant element Si, and O combine to form the most common rock forming mineral group: Silicates

Four Oxygen surrounding a small Silicon atom positioned between them      

to balance this to be neutral we need positively charged cations, such as Fe2+, Mg2+;

Sometimes the tetrahedra may be linked together by sharing Oxygen atoms between Silicon atoms, to form

isolated tetrahedron 4O for 1 Si

single chain 3O for 1 Si

double chain 2O for 1 Si

sheet 2. O for 1Si

complex three dimensional framework 2O for 1 Si

As we go from isolated to the more complex structure there is an increase in the number of oxygen shared.

high silicon content vs.low

Isolated olivin; femg(SiO₄)

Framework quartz; SiO₂

Most common cations balancing in the Silicate structures:

Mg2+

Fe2+ (substitute for each other

Na+

K+ (substitute for each other)

Ca2+

Al3+ (replace silicon)

Silicate minerals:

Ferro-Magnesian minerals

Single tetrahedron

olivine (Mg,Fe)2 SiO4

Single chain

Pyroxene (Mg,Fe)2 Si2O6

Double chain

Amphibole (Ca, Mg)Si4O11(OH)2

Sheet silicates

Non ferromagnesian silicates

Sheet Silicates

Muscovite mica

Clay minerals

complex minerals with sheet silicate structure; very fine grained

products of chemical weathering of other silicate minerals

kaolinite

they are able to absorb water and swell to several times to their normal size.

(milk shake)

Framework Silicates

Feldspars  

 

 

 

Quartz SiO2

The bond between silica-Oxygen is covalent, very strong

Cations to silicate structure ionic---- less strong, resulting in good cleavage.

native elements

gold

silver

copper

diamond

graphite

platinum

sulfides

galena

sphalerite

pyrite

chalcopyrite

cinnabar

oxides

hematite

magnetite

corundum

ice

ilmenite

carbonates

calcite

aragonite

dolomite

siderite

malachite

azurite

sulfates

gypsum

anhydrite

barite

halides

halite

fluorite

sylvite

hydroxides

limonite