Minerals building blocks of rocks

Minerals


Minerals: Building blocks of rocks
To be considered a mineral, a substance
must:
• be a naturally occurring solid
• be formed by inorganic processes
• have a crystalline structure (orderly
molecular arrangement)
• have a specific chemical composition


• An element is a substance that cannot be
broken down into simpler substances by
chemical means
• Minerals are made up of one or more elements


Most abundant elements of the
continental crust
• Common rockforming minerals are
mostly chemical
compounds made up
of these elements
• How do these
elements combine to
make minerals?


Atoms, molecules and ions

• Atoms are the smallest
individual particle that
retains the distinctive
chemical properties of an
element.
• Molecules are the smallest
individual particle that
retains the distinctive
chemical properties of a
chemical compound.
Molecules consists of 2 or
more atoms.
• Ions are atoms or
molecules that have a net
electrical charge. They
attract oppositely-charged
ions to form chemical
compounds.


Crystalline Nature of Minerals
• Crystal: any
substance whose
atoms are
arranged in a
regularly
repeating pattern
• Crystal growth is
often interrupted
due to:

– lack of space
– rapid cooling
rate


Luster: Appearance of a mineral in
reflected light
• Metallic (pyrite)

Nonmetallic: glassy/pearly
(potassium feldspar)


Luster: Appearance of a mineral in
reflected light
• Nonmetallic- waxy
(ex: chert)

• Nonmetallic –greasy
(quartz)


Color
• Often highly
variable for a
given mineral
due to slight
impurities in
crystal
structure

• For example,
quartz (SiO2)
exhibits a
variety of
colors


Other Physical properties of
minerals
• Streak
• Color of a mineral in its powdered form
• Helpful in distinguishing different forms
of the same mineral

• Hardness
• Resistance of a mineral to abrasion or
scratching
• All minerals are compared to a standard
scale, the Mohs Scale of Hardness.


Streak – the color of
a powdered mineral

Figure 2.10


Hardness
• Resistance of a
mineral to

abrasion or
scratching
• All minerals are
compared to a
standard scale
called the Mohs
scale of
hardness


Cleavage
• Tendency to break along planes of
weak bonding
• Produces flat, shiny surfaces
• Described by resulting geometric
shapes, and
– Number of planes
– Angles between adjacent planes


Three examples of perfect
cleavage – fluorite, halite,
and calcite

Copyright © 2006 Pearson Prentice Hall, Inc.


Common
cleavage
directions

Classification of Minerals
Rock-forming minerals
• Common minerals that make up most of
the rocks of Earth’s crust
• Only a few dozen members
• Composed mainly of the 8 elements that
make up over 98% of the continental
crust


8 most common elements


Classification of Minerals
• In most cases, minerals are grouped
according to the major “building
block” in the chemical structure.
• Silicates (SiO44-)
• Oxides (O22-)
• Sulfides (S2-)
• Sulfates (SO42- )
• Carbonates (CO32-)
• Halides (Cl1- , F1- Br1- )
• Native Elements (single element)


Rock-forming Minerals – The Silicate
Group

• Most common mineral
group due to large amounts
of silicon and oxygen in
Earth’s crust
• Basic building block is the
silicate ion: Four oxygen
ions surrounding a much
smaller silicon ion.
• Polymerization: process by
which silicate ions bond to
form more complex ions,
such as rings, chains,
sheets or 3 dimensional
frameworks.


Common Silicate minerals
• Olivine Group
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– High temperature Fe-Mg silicate
– Individual silicate linked together by iron and
magnesium ions
– Forms small, rounded crystals with no cleavage


Common Silicate minerals
• Pyroxene Group
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– Single chain structures involving iron and
magnesium

– Two distinctive cleavages at nearly 90 degrees


Common Silicate Minerals

• Amphibole Group

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– Double chain structures involving a variety of ions
linking the silicate ion
– Two perfect cleavages at non right angles
Hornblende is the most common mineral in the
amphibole group


Common Silicate Minerals
• Mica Group
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– Sheet structures that result in one direction of
perfect cleavage
– Biotite is the common dark colored mica.


Common Silicate Minerals
• Mica Group
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– Sheet structures that result in one direction of
perfect cleavage
– Muscovite is the common light colored mica.

Classification of Minerals
• Common Silicate minerals
• Feldspar Group
– Most common mineral group
– 3-dimensional framework that exhibits two
directions of cleavage at 90 degrees
– (potassium feldspar) (e.g. Orthoclase or
Microcline)
– Plagioclase (sodium and calcium feldspar)
are the two most common members