Rock: aggregate of different minerals
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 lets 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.
Proton: has positive electrical charge
mass of proton is taken as the unit of atomic mass.
Neutron: electrically neutral it has about the same mass as the
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.
Are whole atoms have electric charge??????
Are whole atoms have electric charge??????
They are neutral, when uncombined!!!!!!
Element: large collection of electrically neutral atoms having the same atomic number
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)
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)
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
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, 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.
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
hardness is the measure of a minerals 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.
You can fill it by picking up the mineral. heavier have larger specific gravity
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
malachite- bright green
hematite - red
pyrite - yellow
the color of the mineral in its powdered form. (unglazed porcelan plate streak plate) nonmetallic minerals usually do not have very characteristic streak.
the apparance of light reflected from the surface of the mineral.
4000 existing mineral, even today 40 in each year are discovered.
The ones 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 Earths 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
Fundamental building block:
Fundamental building block:
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.
Therefore the more oxygen shared the percentage of silicon increases:
high silicon content vs.low
Isolated olivin; femg(SiO4)
Framework quartz; SiO2
Most common cations balancing in the Silicate structures:
Fe2+ (substitute for each other
K+ (substitute for each other)
Al3+ (replace silicon)
olivine (Mg,Fe)2 SiO4
Pyroxene (Mg,Fe)2 Si2O6
Amphibole (Ca, Mg)Si4O11(OH)2
Biotite mica K(Mg,Fe)Si4O10(OH)
Non ferromagnesian silicates
complex minerals with sheet silicate structure; very fine grained
products of chemical weathering of other silicate minerals
they are able to absorb water and swell to several times to their normal size.
The bond between silica-Oxygen is covalent, very strong
Cations to silicate structure ionic---- less strong, resulting in good cleavage.