minerals fall 2015
MINERALS
• Introduction
• What Are They?
• Physical Properties & Identification
• Atoms & Elements
• Mineral Groups
Minerals
Introduction
GEOL 131: Minerals - Intro
Eight Most Abundant Elements in Earth’s Crust
GEOL 131: Minerals - Intro
GEOL 131: Minerals - Intro
Some of the Most Abundant Minerals in Earth’s Crust
• Quartz
• Feldspars
• Micas
GEOL 131: Minerals - Intro
Some of the Most Abundant Minerals in Earth’s Crust
• Amphiboles e
• Pyroxenes
• Olivine
What Are They?
GEOL 131: Minerals – What Are They?
Minerals Are:
• Solid
• Naturally occurring
• Inorganic
GEOL 131: Minerals – What Are They?
Minerals Have:
• Well-defined chemical compositions
• Well-ordered atomic structures
Minerals
Physical Properties &
Identification
GEOL 131: Minerals – Physical Properties & Identification
Physical Properties
• Each mineral has a unique set of properties
• Determined by mineral’s chemical composition and atomic structure
• Properties are used to identify unknown minerals
GEOL 131: Minerals – Physical Properties & Identification
Physical Properties Commonly Used in
Identification
• Color
• Streak
• Luster
• Cleavage
• Crystal habit
• Striations
• Hardness
• Effervescence
• Magnetism
GEOL 131: Minerals – Physical Properties & Identification
COLOR
• Easy to observe, but can be misleading
• Impurities can produce different colors
Quartz
GEOL 131: Minerals – Physical Properties & Identification
STREAK
• Color of powdered mineral
• More reliable than “bulk” color
Streak plate
GEOL 131: Minerals – Physical Properties & Identification
LUSTER
• How sample reflects light
• Not the same as color
METALLIC luster
NONMETALLIC luster
GEOL 131: Minerals – Physical Properties & Identification
LUSTER
• How sample reflects light
• Not the same as color
Both of these minerals have a METALLIC luster
GEOL 131: Minerals – Physical Properties & Identification
CLEAVAGE
• How sample cleaves (breaks)
• Always the same for a given mineral
• Three aspects
– Quality
– Number of directions
– Angle
GEOL 131: Minerals – Physical Properties & Identification
CLEAVAGE QUALITY - None
No cleavage: irregular breakage surface
GEOL 131: Minerals – Physical Properties & Identification
CLEAVAGE QUALITY - Good
Note “stair-step” pattern
Good cleavage: somewhat regular breakage surface
GEOL 131: Minerals – Physical Properties & Identification
CLEAVAGE QUALITY – Excellent/perfect
Excellent cleavage: smooth breakage surface
GEOL 131: Minerals – Physical Properties & Identification
# OF CLEAVAGE DIRECTIONS
• A number
• Only applies to good or excellent cleavage quality
GEOL 131: Minerals – Physical Properties & Identification
# OF CLEAVAGE DIRECTIONS - One
One smooth surface
GEOL 131: Minerals – Physical Properties & Identification
# OF CLEAVAGE DIRECTIONS - Two
Two non-parallel smooth surfaces
GEOL 131: Minerals – Physical Properties & Identification
# OF CLEAVAGE DIRECTIONS - Three
Three non-parallel smooth surfaces
GEOL 131: Minerals – Physical Properties & Identification
# OF CLEAVAGE DIRECTIONS - Four
Fluorite
Four non-parallel smooth surfaces
GEOL 131: Minerals – Physical Properties & Identification
CLEAVAGE ANGLE
• Angle between cleavage surfaces
90-degree angle
60-degree angle
120-degree angle
GEOL 131: Minerals – Physical Properties & Identification
CRYSTAL HABIT
• How a mineral grows
• Unusual to see well-formed crystals in nature
– Need space to grow
GEOL 131: Minerals – Physical Properties & Identification
CRYSTAL HABIT
Well-formed crystal faces
Poorly-formed crystals: not enough space
GEOL 131: Minerals – Physical Properties & Identification
CRYSTAL HABIT
• Don’t confuse a crystal face with an excellent cleavage surface
• Crystal face – caused by growth
• Cleavage surface – caused by breaking
GEOL 131: Minerals – Physical Properties & Identification
STRIATIONS
• Thin grooves on mineral’s surface
• Can be hard to see
From facweb.bhc.edu
From www4.uwm.edu
GEOL 131: Minerals – Physical Properties & Identification
HARDNESS
GEOL 131: Minerals – Physical Properties & Identification
EFFERVESCENCE
Dilute hydrochloric acid
(HCl)
If CO
3 ion present, carbon dioxide bubbles will form:
CaCO
3
(calcite) + 2HCl =
H
2
O + CO
2
+ CaCl
2
GEOL 131: Minerals – Physical Properties & Identification
MAGNETISM
• Some iron-rich minerals are magnetic
Magnetite (Fe
3
O
4
) attracting a magnet
GEOL 131: Minerals – Physical Properties & Identification
MINERAL IDENTIFICATION
• Table or flowchart
• Observation of unique properties
• Narrow down possibilities
GEOL 131: Minerals – Physical Properties & Identification
MINERAL
IDENTIFICATION
Minerals
Atoms &
Elements
GEOL 131: Minerals – Atoms and Elements
All Minerals Are Made of Atoms
GEOL 131: Minerals – Atoms and Elements
The Periodic Table of the Elements http://www.ptable.com/
GEOL 131: Minerals – Atoms and Elements
Basic Structure of an Atom
GEOL 131: Minerals – Atoms and Elements
Valence Shells
GEOL 131: Minerals – Atoms and Elements
Atomic Bonds
• Hold atoms together to make mineral crystals
• Formed by electron interaction
• Require filled valence shells
GEOL 131: Minerals – Atoms and Elements
Atomic Bonds
GEOL 131: Minerals – Atoms and Elements
Atomic Bonds
GEOL 131: Minerals – Atoms and Elements
Chemical Composition of Minerals
• Elements present and in what amounts
• Well-defined: Limited or no variation
• Described by mineral’s formula
• Halite (salt): NaCl
GEOL 131: Minerals – Atoms and Elements
Atomic Structure of Minerals
• Arrangement of atoms
• Well-ordered: Repeats in a regular pattern
GEOL 131: Minerals – Atoms and Elements
Atomic Structure of Minerals
• Arrangement of atoms
QUARTZ
GEOL 131: Minerals – Atoms and Elements
Atomic Structure – Diamond vs Graphite
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS
• Silicates (largest group)
• Carbonates
• Sulfates
• Sulfides
• Oxides
• Halides
• Native elements
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
• Largest group
– 90% of Earth’s crust
• Si and O atoms in a tetrahedron
(pyramid)
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
• Oxygen atoms can bond to adjacent tetrahedra in a mineral’s atomic structure
• Forms the “backbone” of the mineral
• Example: single-chain structure
– Each tetrahedron shares two oxygens with adjacent tetrahedra
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
Silicate structures
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
• A silicate mineral’s properties depend partly on its silicate structure
– Hardness: 3-D networks make harder minerals
(quartz)
– Cleavage: sheet structures produce sheet cleavage
(micas)
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
• Example: Hardness
– 3-D frameworks make harder minerals
Quartz
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
• Example: Cleavage
– Sheet structures produce sheet cleavage
Micas
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
• Dark vs. light silicates
– Dark: rich in Fe and Mg
– Light: little Fe or Mg
• Important for igneous rocks (next chapter)
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS - Silicates
• Some common silicate minerals
– Quartz: SiO
2
– Orthoclase feldspar (aka potassium feldspar or Kspar): KAlSi
3
O
8
– Muscovite mica: KAl
2
(AlSi
3
O
10
)(F,OH)
2
– Hornblende: Ca
2
(Mg, Fe, Al)
5
(Al, Si)
8
O
22
(OH)
2
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS – Carbonates
• CO
3 ion
• Effervescence
• Common examples
– Calcite: CaCO
3
– Dolomite: CaMg(CO
3
)
2
– Malachite: Cu
2
CO
3
(OH)
2
Malachite
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS – Sulfates
• SO
4 ion
• Common examples
– Gypsum: CaMgSO
4
*2H
2
O
– Anhydrite: CaMgSO
4
– Barite: BaSO
4
Giant gypsum crystals, Naica Mine, Mexico
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS – Sulfides
• S, no oxygen
• Important metal ores
• Common examples
– Galena: PbS
– Pyrite: FeS
– Chalcopyrite: CuFeS
2
Cubic galena crystals
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS – Oxides
• Oxygen
• No Si, C, or S
• Common examples
– Hematite: Fe
2
O
3
– Magnetite: Fe
3
O
4
– Corundum: Al
2
O
3
Red corundum (ruby)
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS – Halides
• Cl, F, or Br
• Common examples
– Halite (salt): NaCl
– Fluorite: CaF
2
Wieliczka salt mine, Poland
GEOL 131: Minerals – Mineral Groups
MINERAL GROUPS – Native elements
• Any element in pure form
• Common examples
– Sulfur (S)
– Graphite (C)
– Copper (Cu)
End of Minerals chapter
