Minerals and
Rocks
Lecture Outline
 What are minerals?
 Common rock-forming minerals
 Physical properties of minerals
 Basic rock types
 The rock cycle
Minerals
A mineral is a naturally occurring, solid
crystalline substance, generally inorganic,
with a specific chemical composition
 Natural
 Solid
 Atoms arranged in orderly repeating 3D array:
crystalline
 Not part of the tissue of an organism
 Composition fixed or varies within defined limits
Minerals are the “building blocks” of rock
Large individual crystals (rare)
Mass of small grains: each is a crystal,
but grown up against each other
Atomic Structure of Minerals
 NaCl - sodium chloride
Halite
Chemical Bonds: Ionic
 Electrical attraction between ions of opposite charge
 Bond strength increases with the electrical charges of the
ions
 Bond strength decreases as the distance between the
ions increases
 Most minerals are this kind of compound
Ionic Bonding example:
halite
Cation
Na+
Anion
Cl-
Covalent Bonds:
 Electron sharing
 Generally stronger than ionic bonds (e.g., diamond)
Crystallization of Minerals
 Need starting material with atoms that can come
together in the proper proportions
 Growth from a liquid or a gas
 Time and space for crystallization
 Appropriate temperature and pressure
 Examples
 Magma that has cooled below its melting point
 Supersaturated solution --> precipitation
Crystallization of Minerals
 Crystals begin as an initial “seed” - a microscopic
crystal
 Atoms keep being added in a 3D array, repeating the
basic arrangement
 Crystal faces are based on the array structure
Cations and Anions
 Anions are typically large
 Cations are relatively small
 Crystal structure is
determined largely by the
arrangement of the anions
Common cations and anions
Radii given in angstroms; 10-8 cm
Ions can be compound
 So far, we’ve talked about individual atomic ions
 Many common minerals are silicates
SiO4
4-
Complex ions act
as a single ion in
forming crystal
structure
Cation Substitution
 Crystal structure determined by those large anions
 Various cations can substitute for each other in many
minerals
 Same crystal structure
 Different chemical composition
Polymorphs
 Minerals with the same composition, but different
crystal structure.
Common Rock-Forming Minerals
Minerals fall into a small number of related “families” based
mainly on the anion in them
Silicates
 Most abundant minerals in the Earth's crust
 Silicate ion (tetrahedron), SiO44-

Quartz (SiO2), K-feldspar (KAlSi3O8), olivine
((Mg, Fe)2SiO4), kaolinite (Al2Si2O5(OH)4)
Quartz (SiO2)
Silicate structure
 Most of the most common rocks in the crust are silicates
 Silicate tetrahedra can combine in several ways to form
many common minerals
 Typical cations:
K+, Ca+, Na+, Mg2+, Al3+, Fe2+
Different numbers of oxygen ions are shared among tetrahedra
Carbonates
 Cations with carbonate ion (CO32-)
 Calcite (CaCO3), dolomite (CaMg(CO3)2), siderite
(FeCO3), smithsonite (ZnCO3)
 Make up many common rocks including limestone and
marble
 Very important for CCS!
Calcite (CaCO3)
CaCO3 + 2H+ = Ca2+ + CO2 + H2O
Smithsonite (ZnCO3)
Oxides
 Compounds of metallic cations and oxygen
 Important for many metal ores needed to make things
(e.g., iron, chromium, titanium)
 Ores are economically useful (i.e., possible to mine)
mineral deposits
Hematite (Fe2O3)
Sulfides
 Metallic cations with sulfide (S2-) ion
 Important for ores of copper, zinc, nickel, lead, iron
 Pyrite (FeS2), galena (PbS)
Galena (PbS)
Sulfates
 Minerals with sulfate ion (SO42-)
 Gypsum (CaSO4.H2O), anhydrite (CaSO4)
Gypsum
Gypsum
Cave of the Crystals
•1,000 feet depth in the silver
and lead Naica Mine
•150 degrees, with 100 %
humidity
•4-ft diameter columns 50 ft
length
Identification of Minerals
 Chemical composition (microprobes and wet chemical
methods)
 Crystal structure (X-ray diffraction)
 Physical properties
Physical properties
 Hardness
Physical properties
 Hardness
 Cleavage: tendency of minerals to break along flat
planar surfaces into geometries that are determined
by their crystal structure
Cleavage in mica
Cleavage in calcite
Halite (NaCl)
Physical properties
 Hardness
 Cleavage
 Fracture: tendency to break along other surfaces
(not cleavage planes)
Conchoidal fractures
Physical properties
 Hardness
 Cleavage
 Fracture
 Luster (metallic, vitreous, resinous, earthy, etc.)
 Color (often a poor indicator; streak color is better)
 Specific gravity
 Crystal habit (shape)
Rocks
An aggregate of one or more minerals; or a body of
undifferentiated mineral matter (e.g., obsidian); or of
solid organic matter (e.g., coal)
 More than one crystal
 Volcanic glass
 Solidified organic matter
 Appearance controlled by composition and size and
arrangement of aggregate grains (texture)
Rock Types



Igneous
 Form by solidification of molten rock (magma)
Sedimentary
 Form by lithification of sediment (sand, silt, clay,
shells)
Metamorphic
 Form by transformations of preexisting rocks (in
the solid state)
Igneous Rocks
 Intrusive
 Extrusive
Intrusive (plutonic)
 Form within the Earth
 Slow cooling
 Interlocking large crystals
 Example = granite
Extrusive (volcanic)
 Form on the surface of the Earth as a result of volcanic
eruption
 Rapid cooling
 Glassy and/or fine-grained texture
 Example = basalt
Basalt: igneous extrusive
Intrusive and extrusive igneous rocks
Sedimentary Rocks
Origin of sediment
 Produced by weathering and erosion or by
precipitation from solution
 Weathering = chemical and mechanical breakdown of
rocks
 Erosion = processes that get the weathered material
moving
Sediment types
 Clastic sediments are derived from the physical
deposition of particles produced by weathering and
erosion of preexisting rock.
 Chemical and biochemical sediments are precipitated
from solution.
Clastic
Chemical/biochemical
Lithification
 The process that converts sediments into solid rock
 Compaction
 Cementation
Cemented sandstone
Metamorphic Rocks
Regional and contact metamorphism
conglomerate
metaconglomerate
granite
gneiss
The Rock
Cycle
The Rock Cycle