Download Minerals

Chemistry and
Minerals
Atoms, Elements and
Ions
Atom
• is the smallest unit of all substances and
comprised of protons (plus charged) and
neutrons (no charge) located in nucleus
(center) of atom and electrons (minus
charged) which orbit the nucleus
• this structure resembles the solar system
with the sun (protons and neutrons) at the
center and planets (electrons) orbiting the
central portion
Atom
Element
– is a substance comprised of atoms each atom
with the same number of protons but not
necessarily same number of neutrons and
electrons
– there are many different elements (see the
Periodic Table of elements)
• Atomic Number of an Element
– is the common number of protons in the
nucleus of each atom of the element
– examples: 1 proton in each atom of hydrogen
(H) and 92 for the same in uranium (U)
Elements (continued)
• Atomic Mass of an Element
– is the sum of the number of protons and
neutrons in each atom of an element
– examples: any oxygen (O) atom with an atomic
mass of 16 has 8 neutrons and 8 protons in its
nucleus and that for uranium (U) with an
atomic mass of 235 has 92 protons and 143
neutrons
– the aforementioned atoms will have an atomic
mass designation of O16 and U235 respectively
Elements (continued)
• Isotope of an Element
– atoms of an element which have the same
atomic mass belong to the same element
isotope
– stable isotopes are atoms which are not
radioactive which means they do not break
down or decay to form atoms of other elements
– examples of stable isotopes are O16, O17, and
H1
– unstable isotopes are atoms which are
radioactive and decay to form atoms of other
elements
Elements and Isotopes
(continued)
– examples of unstable isotopes are U238, (
which decays to Pb206) and C14(which decays
to N14), or any isotope which has an atomic
number greater than that for bismuth (Bi)
• Atomic Weight of an Element
– is the average of the atomic masses of all the
stable and unstable (radioactive) isotopes of an
element
• Periodic Table of Elements
– a listing of the elements in order of increasing
atomic number left to right and top to bottom
Periodic Table of Elements
Ion
– an ion is a charged atom of an element caused
by the atom having an unequal number of
protons and electrons
• Cation
– is a + (plus) charged atom resulting from the
number of protons exceeding the number of
electrons
– if a sodium (Na) atom with its 11 protons has
lost an electron from the original 11, it then has
10 electrons and becomes a cation since there is
a sufficiency of + charges over - charges
Ion (continued)
• Anion
– is a (-) minus charged atom caused by the
number of electrons exceeding the number of
protons in the atom
– if a chlorine (Cl) atom with its characteristic 17
protons has acquired an extra electron from the
original 17 it has 18 electrons and becomes an
anion since it is deficient in the number of
protons compared to the number of electrons
Chemical Bonds
Chemical Bonds
• are forces which hold atoms together
• the type of bond between atoms can
determine mineral properties including
physical and chemical properties
• there are three main types of chemical
bonds in minerals
Chemical Bonds (contin)
• Ionic Bond
– is an attraction between atoms caused by a
transfer of electron(s) from one atom to another
– an example is atoms in halite (NaCl); each
sodium (Na) atom transfers one electron to a
chlorine atom
– this causes each Na atom to become plus
charged and each chlorine atom minus charged
resulting in an attraction of the atoms
• Covalent Bond
– is a force between atoms caused by a sharing
of electron(s) between atoms
Ionic Bond
Covalent Bond
Covalent Bonds (contin)
– an example of a covalent bond is in the atoms
of graphite (C) ; each atom of carbon shares
electrons with another carbon atoms
– since one carbon atom has all of the shared
electrons at one instant it is minus charged
while the other atom is deficient in electrons
and plus charged
• Metallic Bond
– is a force caused by electrons moving freely
between atoms
– an example of this is electrons of iron (Fe)
atoms moving between iron atoms
Ionic Bonds (cont)
– this flow of electrons results in good electrical
conductivity in substances
– often a bond between atoms is a mixture of the
above cited bonds
Minerals
Minerals
• Definition
–
–
–
–
naturally occurring
inorganic solid substance
having an orderly arrangement of atoms
having a consistent chemical composition that
may vary within specific limits
• Explanations
– man made diamonds are not naturally occurring
therefore are not minerals
– natural petroleum and coal are referred to as
mineral resources but are organic in composition
Minerals-Explanations
(contin)
– ice is a mineral if formed in nature
– a mineraloid is a substance which conforms
with 1, 2, and 4 above but does not have an
orderly arrangement its atoms
– there are two major differences between
minerals and rocks:
• 1. minerals can have crystal form but rocks
cannot (any mineral can form a crystal shape
if it has adequate space in which to grow)
• 2. minerals occur in smaller or limited
amounts while rocks occur in large massive
amounts
Minerals (contin)
• Origin and Occurrence of Minerals
– formed during the rock forming process and comprise
an essential part of the rock
– formed in cracks, fractures, or holes within the rock
after the formation of the rock
• Mineral Classification
– minerals are classified into classes (groups) based on
chemical composition
– based primarily on the anion type present in the
mineral
– 1. Non-silicate minerals
• Oxides--oxygen (O) is the major mineral anion
Mineral Classes (contin)
• with examples as hematite (Fe2O3), and magnetite
(Fe3O4)
• 2. Sulfides--sulfur (S) is the major anion with
examples as galena (PbS), pyrite (FeS2), and
sphalerite (ZnS)
• 3. Sulfates--sulfur (S) and oxygen (O) together
form the major (complex) anion with examples as
barite (BaSO4) and gypsum (CaSO4.2H2O)
• 4. Native elements--atoms of one element with
examples as mineral sulfur (S), and graphite (C)
• 5. Halides--Cl, Br, F, or I is the major anion with
examples as halite (NaCl) and fluorite (CaF2)
Mineral Classes (contin)
• 6. Carbonates--carbon (C) and oxygen (O) together
form the major (complex) anion with examples as
calcite (CaCO3) and dolomite-CaMg(CO3)2
• page 53 in your text shows a Table of Common
Non-silicate Minerals
Mineral Classes (contin)
– 2. Silicate Minerals
• Silicon (Si) and oxygen (O) together form the
major (complex) anion
• this is the single most abundant class (group) of
mineral
• all igneous rocks, most sedimentary rocks and all
but one metamorphic rock are comprised of silicate
mineral aggregates
• the tetrahedron is the “basic building block” of the
silicate mineral structure
• see page 48 for common silicate minerals and
structures
Minerals (contin)
• Identification of Minerals by Name
– 1. Use of Physical Properties
• Color-- colors can differ from one sample to
another of the same mineral
• Luster--metallic and nonmetallic
• Streak color--color of the powder of a mineral on a
porcelain (streak) plate
• Hardness
• Cleavage or fracture--a mineral will break apart in a
consistent pattern (cleavage) or it will not and
shatter like glass (fracture)
• Other special physical characteristics
Minerals ID by Name (contin)
– 2. Use of Chemical Analysis
• The element composition of a mineral gives
important information when trying to determine the
name of a mineral
– 3. Use of X-ray Analysis
• the atomic arrangement in a mineral is like a
genetic code for that mineral and Xray analysis can
determine that code
• Radioactivity in Minerals
– allows the absolute age of a rock to be determined
Radioact. in Minerals (contin)
– some atoms of elements comprising the chemical
makeup of minerals in rocks are radioactive
– 1. Radiation Particles in Minerals
• radioactive particles are emitted from the nucleus of
atoms when atoms of elements decay to form other
elements
• most common are alpha particles (plus charged)
,beta particles (minus charged), and gamma particles
(no charge)
– 2. Radioactive Parent and Daughter Isotopes
• parent atoms are radioactive and decay eventually to
stable atoms of an element called a daughter
Parents and Daughter (contin)
• examples of radioactive parent and stable daughter
isotopes are: U238 and Pb206; K40 and Ar40; C14
and N14
– 3. Absolute Age Determination Method
• the amounts (number of atoms) of parent and
daughter are determined by a mass spectrograph-based on the amounts of each the age of the rock
can be determined
• in order for the determination to be successful and
accurate the minerals in which the daughter and
parent atoms occur must be formed at the same time
as the rock
Absol. Age Determ. Method (contin)
• the amounts of parent and daughter cannot be
externally introduced or extracted from the rock
whose age is to be determined
• many sedimentary rocks are comprised of
accumulations of mineral or rock particles from
previously formed rocks hence the amounts of
parent and daughter represent the time of formation
of that previously formed rock
• most absolute age determinations are obtained using
igneous rocks
• Important Uses of minerals
– 1. Gemstones
Gemstones (contin)
• is a rare variety of a mineral
• possesses a quality of beauty and is usually hard
• rubies (red) and sapphires (blue) are gemstone
varieties of corundum
• emeralds (green) and aqua marine are gemstones of
beryl
• amethyst and cat’s eye are gemstones of quartz
– 2. Elements Extracted from Minerals
• barium (Ba) from barite (BaSO4); iron (Fe) from
hematite (Fe2O3); lead (Pb) from galena (PbS); zinc
(Zn) from sphalerite (ZnS)
Mineral- Special Uses(contin)
– 3. Other Special Uses
• use of graphite in pencils, sulfur in matches,
talc as baby powder, etc.