Download Chapter 3: Atoms, Elements, Minerals, Rocks

Chapter 3: Atoms, Elements,
Minerals, Rocks: Earth’s Building
Materials
Introduction : What Is A Mineral?
 The four components of our planet:
 Atom
- The smallest individual particle that retains the
distinctive properties of a chemical element.
 Element
- Any of the 92 naturally occurring fundamental
substances into which matter can be broken down
chemically (for example, hydrogen, oxygen, carbon,
silicon, lead).
Introduction : What Is A Mineral? (2)
 Mineral
- Naturally formed, inorganic, solid material with a
specific chemical composition and a characteristic
crystalline structure.
 Rock
- Naturally formed, coherent mass of one or more
minerals, sometimes including organic debris.
Mineraloids
 Mineraloid
 Some naturally occurring solid compounds do not
meet the definition of a mineral because they
lack:
- a definite composition, or
- a characteristic crystal structure, or
- both.
Key Characteristics of Minerals
 Minerals have two key characteristics.
 Composition:
- The chemical elements that compose a mineral, and
their proportions.
 Crystal structure:
- The organized way in which the atoms of the elements
are packed together in a mineral.
Composition of Minerals
 A few minerals are composed of a single element
(examples are diamond, graphite, gold, copper, and
sulfur).
 Most minerals are compounds, containing more
than one element.
 Chemical elements are the most fundamental
substances into which matter can be separated by
chemical means.
SALT: Mineral or Element?
 Salt (NaCl) is not an element, because it can be
separated into sodium and chlorine.
 Sodium (Na) and chlorine (Cl) cannot be broken
down further chemically, so each is an element.
 Each element is identified by a symbol.
Atoms: Elementary Structure
 Protons and neutrons are dense, and form the
nucleus (core) of an atom.
 Protons have positive electric charges.
 Neutrons have no charge.
 The nuclei of atoms always have a positive charge.
 Electrons, which have negative electrical charges
that balance exactly the positive charges of
protons, move in orbitals around the nucleus.
Figure 3.1
Atomic Number
 The number of protons in the nucleus gives each
atom its special chemical characteristics.
 Elements are catalogued by atomic number.
 Uranium, with 92 protons in its nucleus, has the
highest atomic number of the naturally
occurring elements.
 Ununquadium,the heaviest synthesized element,
reported early in 1999, has an atomic number of
114.
Isotopes
 Mass number: the sum of the numbers of
neutrons and protons in an atom.
 Isotopes: atoms with the same atomic number
but different mass numbers (for example,
carbon-12, carbon-13, and carbon-14 all have six
protons per atom, and thus have the same atomic
number).
Energy-Level Shells
 Electrons move around the nucleus of an atom in
complex three-dimensional patterns called
orbitals.
 Groupings of orbitals are called energy-level
shells.
 Electrons require different amounts of energy to
orbit in different energy-level shells.
Ions
 Ions: Atoms that have lost or gained an electron.
 Cation: An atom that has lost an electron and
thus has a positive charge.
 Anion: An atom that has gained an electron and
thus has a negative charge.
Compounds
 Chemical compounds form when atoms of
different elements combine in a specific ratio.
 Properties of compounds are quite different from
the properties of their constituent elements.
Figure 3.2
Bonding
 A molecule is the smallest unit that has the
distinctive chemical properties of a compound.
 A molecular compound always consists of two or
more kinds of atoms held together.
 The force that holds the atoms together in a
compound is called bonding.
 Bonding determines the physical and chemical
properties of a compound.
Four Types of Bonding (1)
There are four important kinds of bonds:
 Ionic bonding: electron transfers between atoms
produce cations and anions.
 Covalent bonding: some atoms share electrons
rather than transferring them, creating a strong
bond.
- Elements and compounds with covalent bonding tend to
be strong and hard.
- The sparkle that makes diamonds attractive gems is
due to covalent bonding.
Four Types of Bonding (2)
 Metallic bonding: closely packed atoms share
electrons in higher energy-level shells among
several atoms.
- Because the electrons are loosely held, they can drift
from one atom to another.
 Van der Waals bonding: weak secondary
attraction between certain molecules formed by
transferring electrons.
- Much weaker than ionic, covalent,or metallic bonding.
- Graphite and talc.
Figure 3.3 A
Figure 3.3 B
Figure 3.4
Figure 3.5
Complex Ions
 Two or more kinds of ions form such strong
covalent bonds that the combined atoms act as if
they were a single entity.
 Such a strongly bonded unit is called a complex
ion.
 Calcite (CaCO3)
 Gypsum (CaSO42H2O)
Periodic Table of Chemical Elements
(1)
 Dmitri Mendeleev (1834-1907) developed the
Periodic Table.
 Within rows, elements increase in atomic
number from left to right.
 Elements within each column have the same
number of electrons in their outermost energylevel shell.
Periodic Table of Chemical Elements
(2)
 All elements in the first column easily give up the
lone outer-shell electron to form cations (H+,
Li+,etc.).
 The farthest columns to the right contains the six
elements that have full energy-level shells.
 These are called noble gases because they have no
tendency to gain or lose electrons and thus no
tendency to form compounds.
Figure 3.6
Crystal Structure of Minerals
 The atoms in most solids are organized in
regular, geometric patterns, called the crystal
structure.
 Solids that have a crystal structure are said to be
crystalline.
 Ice in a glacier meets the definition of a mineral.
 Solids that lack crystal structures are
amorphous.
 glass and amber.
Ionic Substitution
 Ionic substitution is the substitution of one ion
for another in a compound.
 The bonding in most common minerals is ionic.
 Ionic substitution depends upon:
 Crystal structure;
 Ion size;
- commonly expressed as ionic radius (distance from the
center of the nucleus to the outermost shell of orbital
electrons);
 Ion electrical charge.
Figure 3.7
Figure 3.8
Figure B3.1
Figure B3.2
Crystal Form
 Crystal form
 Crystal: any solid body that grows with planar
surfaces.
 The interfacial angle in any crystalline structure
remains constant.
Figure 3.10
Figure 3.12
Growth Habit and Polymorphism
 Growth habit:
- The characteristic crystal form of each mineral.
 Polymorphism:
- Some elements and compounds form two or more
different minerals:
- C
Graphite, Diamond
- CaCO3
Calcite, Aragonite
- FeS2
Pyrite, Marcasite
- SiO2
Quartz, Cristobalite
Cleavage
 Cleavage is the tendency to break in preferred
directions along bright, reflective planar
surfaces.
 A cleavage surface is a breakage surface,
whereas a crystal face is a growth surface.
 The planar directions along which cleavage
occurs are governed by the crystal structure.
 They are planes along which the bonding between
atoms is relatively weak.
Figure 3.13
Luster
 Luster is the quality and intensity of light
reflected from a mineral.
 The most important lusters are:





Metallic (polished metal surface).
Vitreous (glass).
Resinous (resin): the look of dried glue or amber.
Pearly (pearl): the iridescent look of a pearl.
Greasy (as if the surface were covered by a film of
oil).
Color and Streak
 Color is determined by several factors, but its
main cause is chemical composition.
 Unreliable for identification.
 Streak is the thin layer of powdered material left
when a specimen is rubbed on an unglazed
ceramic plate.
 Much more reliable than color for identification.
Hardness and the Mohs Scale
 Hardness is a mineral’s relative resistance to
scratching.
 The Mohs relative hardness scale uses ten
minerals, each with its distinctive hardness:
 scale indicate relative hardness.
Figure 3.16 A
Figure 3.16 B
Figure 3.16 C
Figure 3.18
Hardness and the Mohs Scale (2)
 We test relative hardness by using common
objects:
 copper penny,equivalent to fluorite’s hardness of
4.
 steel knife blade, equivalent to feldspar’s
hardness of 6.
Density and Specific Gravity
 Density is mass per unit volume.
 Minerals with a high density, such as gold,
contain atoms with high mass numbers that are
closely packed.
 Minerals with a low density, such as ice have
loosely packed atoms.
 The unit of density is gram per cubic centimeter
(g/cm3).
Specific Gravity
 Density is easily measured using the property
called specific gravity.
 Specific gravity is the weight of a substance in air
divided by the weight of an equal volume of pure
water.
 Specific gravity is a ratio of weight.
Mineral Properties and Bond Types
 Minerals properties depend strongly on the
kinds of bonds present.
 Ionic and covalent bonds are strong, making
minerals hard and strong.
 Metallic and van der Waals bonds are much
weaker.
Common Minerals in Earth’s Crust
 Only 12 elements occur in the continental crust
in amounts greater than 0.1 percent by weight.
 These 12 elements make up 99.23 percent of the
crustal mass.
 The crust, therefore, is constructed mostly of a
limited number of minerals.
 Approximately 4,000 minerals have been
identified, but only about 30 are commonly
encountered.
Figure 3.19
Three Mineral Groups
 Silicate minerals (SiO4)4-, the most abundant in
Earth’s crust.
 Carbonate (CO3)2-, phosphate (PO4)3-, and
sulfate (SO4)2- minerals.
 Ore minerals, sulfides (S2-) and oxides (O2-) that
contain valuable metals.
Silicates: The Largest Mineral Group
 Two elements, oxygen and silicon, make up more
than 70 percent of the weight of the continental
crust.
 Polymerization is the creation of compounds by
accepting or sharing electrons.
 Linking silicate tetrahedra by oxygen sharing
results in huge anions.
 It produces endless chains.
Figure 3.20
Figure 3.21
Figure 3.22
Olivines and Garnets
 Two very important rock-forming mineral
groups, the olivines and the garnets, have crystal
structures in which the silicate tetrahedra are
isolated.
 Olivine is among Earth’s most abundant mineral
groups, a very common constituent of igneous
rocks in oceanic crust and the upper part of the
mantle.
Figure 3. 23 A
Olivines and Garnets (2)
 Olivine occurs in such flawless and beautiful
crystals that is used as a gem, peridot.
Chains: Pyroxenes and Amphiboles
 One of the most important mineral groups, the
pyroxenes, contains single-chain linkages.
 The most common pyroxene is called augite.
 A very common and important family of
minerals, the amphiboles, contains double
chains.
 The most common of the amphiboles is called
hornblende.
Chains: Pyroxenes and Amphiboles
 The pyroxenes and the amphiboles are hard to
tell apart.
 The cleavages in pyroxene are right angles (90o).
 The cleavages in amphibole are at 120o.
Figure 3.23
Sheets: Clays, Micas, Chlorites, and
Serpentines
 Kaolinite, Al4Si4O10(OH)8, is one of the most
common clays.
 Muscovite, KAl2(Si3Al)O10(OH)2, is a common
mica.
 Chlorite, which contains Mg2+ and Fe2+ cations,
is usually greenish in color.
Figure 3. 25
Sheets: Clays, Micas, Chlorites, and
Serpentines (2)
 The serpentine group consists of three
polymorphs with the formula Mg6Si4O10(OH)8.
 Chrysotile is the white asbestos of commerce.
Figure 3.24
Quartz
 Quartz is pure SiO2.
 Forms six-sided crystals.
 Found in many colors.
 The colors come from minute amounts of iron,
aluminum,titanium, and other elements present
by ionic substitution.
 Fine grain forms of quartz are called chalcedony:
- Agate
- Flint (gray)
- Jasper (red)
The Feldspar Group — Most Common
Minerals in Earth’s Crust
 Feldspar:
 The most common mineral group in Earth’s
crust.
 Accounts for about 60 percent of all minerals in
the continental crust.
 Feldspar and quartz constitute 75 percent of the
volume of the continental crust.
 Feldspar has a structure formed by
polymerization.
Figure 3. 26
Figure 3. 28
The Carbonates Group
 Carbonates:
 The carbonate anion, (CO3)2-, forms three
common minerals:
- Calcite.
- Aragonite.
- Dolomite.
 Calcite reacts vigorously to HCl.
Figure 3.29
The Phosphate and Sulfate Mineral
Groups
 Phosphates:
 Apatite is the most important phosphate mineral.
- Contains the complex anion ((PO4)3-.
- Common mineral in many varieties of igneous and
sedimentary rocks.
- Main source of the phosphorus used for making
phosphate fertilizers.
The Phosphate and Sulfate Mineral
Groups (2)
 Sulfates:
 All sulfate minerals contain the sulfate anion,
(SO4)2 Only two are common:
- Anhydrite(CaSO4);
- Gypsum (CaSO4.2H2O).
Gypsum is the raw material used for making plaster.
The Ore Mineral Group—Our Source
for Metals
 Sulfides:
 Pyrite (FeS2) and pyrrhotite (FeS) are the most
common.
 Galena (PbS), sphalerite (ZnS), chalcopyrite
(CuFeS2).
 Familiar metals extracted from sulfide ore
minerals are cobalt, mercury, molybdenum, and
silver.
Oxides
 Oxides;
 The iron oxides, magnetite (Fe3O4) and hematite
(Fe2O3), are the two most common oxide minerals.
- Hematite is red when powdered.
 Other oxide ore minerals are:
- Rutile (TiO2), the principal source of titanium;
- Cassiterite (SnO2), the main ore mineral for tin;
- Uraninite (U3O8), the main source of uranium.
Oxides (2)
 Other metals extracted from oxide ore minerals
are chromium, manganese, niobium, and
tantalum.
Minerals Give Clues To Their
Environment Of Formation (1)
 Scientists are able to determine the temperature
and pressures at which carbon will form a
diamond or form graphite, its polymorph.
 Diamonds were at one time subjected to
pressures and temperatures equivalent to those
in the mantle at least 150 km below Earth’s
surface.
Figure 3.31
Minerals Give Clues to Their
Environment of Formation (2)
 Clues to climate:
- Regolith is the blanket of loose rock particles that
covers Earth.
- Some minerals form in regolith during the weathering
process.
- We can decipher past climates from the kinds of
minerals preserved in sedimentary rocks.
 Clues to seawater composition:
- The content of past seawater can be determined from
minerals formed when the seawater evaporated and
deposited its salts.
Rocks: Mixtures of Minerals
 Igneous rocks
 Formed by solidification of magma.
 Sedimentary rocks
 Formed by sedimentation of materials
transported in solution or suspension.
 Metamorphic rocks
 Formed by the alteration of preexisting
sedimentary or igneous rocks in response to
increased pressure and temperature.
Distinguishing The Three Rock Types
The differences among rock types are identified
by two features.
 Texture:
- The overall appearance of a rock due to the size, shape,
and arrangement of its constituent mineral grain.
 Mineral assemblage:
- The type and abundance of the minerals making up a
rock.
Texture and Mineral Assemblage
 A systematic description of a rock includes both
texture and mineral assemblage.
 Megascopic textural features of rocks are those
that we can see with the unaided eye.
 Microscopic textural features of rocks are those
that require high magnification to be viewed.
Figure 3.32 A
Figure 3.32 B
Figure 3.32 C
Figure 3.32 D
Mineral Concentration
 The two most common processes of
concentration of a mineral are:
 Vapors are released by a cooling body of magma.
 A hot saline solution, such as heated seawater,
reacts with and alters a rock, and in the process
extracts the scarce metals.
- As such a solution cools the metals are deposited in
veins.
Figure 3.33
Figure 3.34