Download 5.2 Composition and Structure of Minerals

5.2 Composition
and Structure of
Minerals
Objectives:
1) Identify the characteristics of minerals,
2) Explain how minerals form.
3) List the physical characteristics of minerals that
are influenced by their crystalline structure.
What is a Mineral?
• Mineral: has 5
characteristics
• Occurs naturally
• Solid
• Definite chemical
composition
• Atoms are arranged in
an orderly pattern
• Inorganic (never alive)
What is a Mineral? Cont’d
• 8 elements make up
98.5% of the Earth’s
crust
• Most common
minerals
• Oxygen, silicon,
aluminum, iron,
calcium, sodium,
potassium, magnesium
What is a Mineral? Cont’d
• More than 90% of the
minerals in Earth’s crust are
compounds containing
oxygen and silicon
• Most minerals are
compounds
• Native elements: minerals
made of single elements
• Silver, copper, sulfur,
diamond
• Rocks: mixtures of
minerals
How Minerals Form
• 4 ways to create
minerals
•
•
•
•
Magma
Heat
Pressure
Chemical action
• Creating crystals lab
Structure of Minerals
• Crystal: a regular
geometric solid with
smooth surfaces
called crystal faces
Crystal Structure
• The arrangement of ions, molecules, or atoms in
any mineral determines the shape of the crystal
• Each type of mineral has its own crystal form
Crystal Structure Cont’d
• The angle at which crystal faces meet is a
characteristic for each type of mineral
• Used to help identify the mineral
Crystal Structure Cont’d
• If space is limited when a mineral is forming, there may
not be enough room for crystal faces to develop fully, or
“grow”
• The mineral fills the available space
• Still crystalline, but faces are not visible
Crystal Structure Cont’d
• Crystals have 6 basic types of shapes
• Crystallographic axes: Imaginary lines used to
distinguish the 7 systems of crystal shapes
• Each axis passes through the center of the crystal
Silicates
• Silicates: minerals that
are compounds
including silicon and
oxygen
• May also contain 1 or
more metallic elements
• Few do not contain metal
• >90% of the minerals in
Earth’s crust
Silicates Cont’d
• Silica tetrahedron:
the basic building
block of a silicate
• 4 oxygen atoms packed
closely around a
silicon atom
• Named for its shape
Crystal Structure and
Physical Properties
• Minerals are solid b/c
of crystalline
structures
• Atoms, ion, and
molecules are closely
packed by strong
chemical bonds
Crystal Structure and
Physical Properties
Cont’d
• High temperatures
breaks the bonds and
causes minerals to melt
then to vaporize
• The temperatures at
which a mineral melts
and vaporizes are
characteristic of the
mineral
• Can sometimes identify a
mineral
Crystal Structure and
Physical Properties
Cont’d
• Cleavage: tendency
to split along definite
planes
• Splits along weak
bonds between atoms,
ions, or molecules of
the mineral
Crystal Structure and
Physical Properties
Cont’d
• Hardness of a mineral
depends on the
arrangement of its
ions, atoms, or
molecules and on the
strength of the
chemical bonds
between them
Crystal Structure and
Physical Properties
Cont’d
• Density depends on
the masses of the
atoms in the mineral
but also on how they
are arranged
5.2 Exit Ticket
• Answer the following
questions.
• Use complete
sentences.
• You may NOT use your
book. You MAY use
your notes.
• This is a quiz grade.
1) Identify the
characteristics of
minerals,
2) Explain how minerals
form.
3) List the physical
characteristics of
minerals that are
influenced by their
crystalline structure.