NOTES UNIT 2 MINERALS
Topic 1 : Definitions of Minerals-The Building Blocks of Rocks.
Rock- An aggregate of one or more minerals.
Mineral- a naturally occurring inorganic solid with an orderly internal
structure (atoms arranged in a definite pattern), with a definite chemical
composition that may vary within specific limits.
Topic 2: Minerals: Chemical Compounds Composed of Atoms of Various
Elements.
Minerals are chemical compounds composed of atoms of various elements.
Atomic Structure:
Building blocks of atoms
Nucleus-dense central region of the atom
Protons-positively charged; one unit of mass.
Neutrons-neutral particles; one unit of mass.
Energy levels (shells)-clouds of electrons at different distances from
the nucleus.
Electrons-negatively charged; negligible mass; orbit the
nucleus.
Each shell can contain only a certain number of electrons.
The more electrons, the more energy-level shells.
Atomic number=number of protons= number of electrons.
Defines the element.
Normally an atom of an element is electrically neutral.
If electrons are stripped from the atom (or added to the atom),
the atom is ionized =ion.
Bonding
Elements combine through bonds to form compounds.
Bonding is the result of electrical forces between atoms.
Outermost electrons (outermost energy-level shell) are
involved in bonding.
During bonding an atom seeks to fill its outermost energy-level
shell.
Electrons involved in bonding are called valence electrons.
Ionic bonds
One or more valence electrons are transferred from one atom
to another "Electron exchange"
Atoms become ions
Covalent bonds
Ono or more valence electrons are shared between atoms
"Electron sharing"
Atomic mass=number of protons+ number of neutrons
Atoms of the same elements commonly have varying number
of neutrons in the nucleus, and therefore different atomic
masses.
Atoms of the same elements with different number of
neutrons are called isotopes of that element.
Topic 3: Structure of Minerals
A mineral is:
An orderly array of atoms.
Chemically bonded
Forms a crystalline structure
Each mineral has its own unique crystalline structure.
The crystalline structure is electrically neutral.
Polymorphs are different minerals with the same chemical composition.
Different crystalline structures.
Different physical properties.
Phase change is a change in structure with no change in composition.
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Topic 4: Physical Properties of Minerals
Crystal form-reflects internal atomic structure
Luster
Color
Streak-color of the powder
Hardness-ability to scratch
Cleavage-fracture along planes between weakly bonded atoms in the
crystalline structure.
Fracture
Specific gravity or density- mass per unit volume
Topic 5: Mineral Groups
There are nearly 4,000 minerals.
The rock -forming minerals are most important to geology.
Eight dominant elements (oxygen, silicon, iron, calcium, sodium,
potassium, and magnesium).
Silicates the dominant rock-forming mineral group.
Native elements: Gold, Silver, Copper, Graphite, Diamond, and
Platinum.
Oxides: Hematite, and Magnetite.
Sulfides: Chalocpyrite, and pyrite
Sulfates: Gypsum.
Halides: Halite and Fluorite.
Carbonates: Calcite
Hydroxides: Bauxite.
Phosphates: Apatite
Silicate minerals:
Most silicates form when rock cools from magma.
The temperature and pressure environment, and the chemical
composition of the molten rock largely determines the actual
minerals which are produced during crystallization.
Olivine and pyroxenes form at higher temperatures.
Quartz forms at lower temperatures.
Some silicates form during metamorphism such as garnet.
Ferromagnesian minerals (mafic): Have relatively large percentage of
Fe and Mg anions.
Ex. Olivine, pyroxenes, hornblend, and biotite mica.
Non-ferromagnesian minerals (silicic)
Have relatively more Si, Al, Na, K
Quartz, feldspar, muscovite mica, clays
Pagioclase
Non-silicate minerals: hematite, magnetite, pyrite, calcite.