Matter and Minerals
Matter
Elements and the Periodic Table
 Elements are the basic building blocks
of minerals.
 Over 100 elements are known.
Matter
Atoms
 Smallest particles of matter
 Have all the characteristics of an element
 The nucleus is the central part of an atom
and contains
• protons, which have positive electrical charges
• neutrons, which have neutral electrical charges
Matter
Atoms
 Energy levels, or shells
• surround the nucleus
• contain electrons—negatively charged particles
 The atomic number is the number of protons
in the nucleus of an atom.
Model of an Atom
Matter
Isotopes
 Isotopes of an element have the same number
of protons but varying numbers of neutrons.
 Have different mass numbers: the sum of the
neutrons plus protons
 Many isotopes are radioactive and emit energy
and particles.
 The mass number is the number of neutrons and
protons in the nucleus of an atom.
Matter
Why Atoms Bond
 When an atom’s outermost energy level
does not contain the maximum number
of electrons, the atom is likely to form a
chemical bond with one or more atoms.
• A compound consists of two or more
elements that are chemically combined in
specific proportions.
• An ion is an atom that gains or losses
electrons.
Matter
Types of Chemical Bonds
1. Ionic bonds form between positive and
negative ions.
2. Covalent bonds form when atoms share
electrons.
3. Metallic bonds form when metal ions
share electrons.
Minerals: the building blocks of rocks
• Definition of a Mineral:
 naturally occurring
 inorganic
 solid
 characteristic crystalline structure
 definite chemical composition
How do we identify minerals?
•
Physical properties:







Color
Luster
Hardness
Crystal shape
Cleavage
Specific gravity
Other
Physical Properties of Minerals
•
Color:
– Most obvious, but often misleading
– Different colors may result from impurities
Example:
Quartz
Physical Properties of Minerals
•
Color:
Streak – color of a mineral in powdered form
(used for metallic minerals)
Obtained by scratching
a mineral on a piece of
unglazed porcelain.
Example:
Hematite
Streak
• Red chalk on a chalk board makes
red marks. White chalk makes
white marks.
• Not all minerals work this way.
When some minerals are scratched
along a ceramic streak plate, it
creates a different color.
Gold
• When gold is run
across a streak
plate it makes a
yellowish-gold
color.
• That makes
sense.
Pyrite or “Fool’s Gold”
• When pyrite is run
across a streak plate,
it has a black or dark
green streak.
• Pyrite is not worth
much money, while
gold is worth a lot.
They look alike, so
miners call it fool’s
gold.
Hematite
• Hematite’s color is
grey, but its streak is
red.
• Hema means blood.
• The mineral was
named hematite
because it looked like
it was bleeding when
it was taken across a
streak plate.
One mineral
property we will
not use…
COLOR
A mineral can be many different
colors. Below is Mica.
Many minerals can be the same color. Below are
gold colored minerals. Which one is gold?
The answer…
None of them were
real gold.
Just like with people…
Outside color does not tell you
much about the important
characteristics.
Physical Properties of Minerals
•
Luster:
– How a mineral surface reflects light
– Two major types:
• Metallic luster
• Non-metallic luster
Metallic
example:
Galena
Non-metallic
example:
Orthoclase
Pyrite (Fool’s Gold) Displays
Metallic Luster.
Physical Properties of Minerals
•
Hardness:
– How easy it is to scratch a mineral
– Mohs Scale of Hardness
• relative scale
• consists of 10 minerals, ranked 1 (softest)
to 10 (hardest)
Mohs Scale of Hardness
Hardest (10) – Diamond
Softest (1) – Talc
Common objects:
- Fingernail (2.5)
- Copper penny (3.5)
- Wire nail (4.5)
- Glass (5.5)
- Streak plate (6.5)
Hardness
• Is measured by how easy it is to
scratch.
• Geologists order the hardness by…
1. Scratched by a fingernail.
2. Scratched by a penny.
3. Scratched by a nail.
4. Scratched by a diamond.
These are not all of the tools geologists
use, but it will work for our
experiment.
Gypsum is soft, it can be
scratched by a fingernail.
Calcite is soft, but a little harder
because it cannot be scratched by a
fingernail, but it can be scratched
by a penny.
Fluorite is harder. It can be
scratched by a nail, but not a
penny or fingernail.
Diamonds are the hardest
mineral, so it scratches every
mineral.
Physical Properties of Minerals
•
Crystal shape (or form):
– external expression of a mineral’s internal
atomic structure
– planar surfaces are called crystal faces
– angles between crystal faces are constant for
any particular mineral
Quartz
Pyrite
Physical Properties of Minerals
•
Cleavage vs. Fracture:
– The way a mineral breaks
– Cleavage: tendency of a mineral to break
along planes of weakness
– Minerals that do not exhibit cleavage are said
to fracture
Do not confuse cleavage planes with crystal faces!
Crystal faces are just on the surface and may not
repeat when the mineral is broken.
Physical Properties of Minerals
•
Cleavage is described by:
– Number of planes
– Angles between adjacent planes
– These are constant for a particular mineral
Physical Properties of Minerals
•
Cleavage (1 direction):
Example: mica
Mica Has Cleavage in One Direction
Physical Properties of Minerals
•
Cleavage (2 directions):
orthoclase
amphibole
Physical Properties of Minerals
•
Cleavage (3 directions):
halite
calcite
Physical Properties of Minerals
•
Cleavage (4 directions):
fluorite
Physical Properties of Minerals
•
Fracture:
– minerals that do not exhibit cleavage are said to
fracture
– smooth, curved
surfaces when
minerals break in a
glass-like manner:
conchoidal fracture
Quartz
Conchoidal Fracture
Physical Properties of Minerals
•
Specific gravity:
– weight of a mineral divided by weight of an
equal volume of water
– metallic minerals tend to have higher specific
gravity than non-metallic minerals
Galena
SG=7.5
Quartz
SG=2.67
Physical Properties of Minerals
•
Other properties:
– reaction with hydrochloric acid (calcite fizzes)
– taste (halite tastes salty)
– feel (talc feels soapy, graphite feels greasy)
– magnetism (magnetite attracts a magnet)
Mineral Groups
•
Rock-forming minerals
– ~30 common minerals make up most rocks in
Earth’s crust
– Composed mainly of the 8 elements that
make up over 98% of the crust
Mineral Groups
Element Abundances
SILICATES
Silica
(SiO4)4-
Common cations that
bond with silica anions
All others:
1.5%
Mineral Groups
•
•
Silicates (most abundant)
Non-silicates (~8% of Earth’s crust)
–
–
–
–
–
–
Oxides
Carbonates
Sulfides
Sulfates
Halides
Native elements
O2(CO3)2S2(SO4)2Cl-, F-, Br(single elements; e.g., Au)
Mineral Groups
Non-ferromagnesian
Silicates (K, Na, Ca, Al)
Ferromagnesian
Silicates (Fe, Mg)
Oxides
Carbonates
Sulfides/sulfates
Native elements
Mineral Groups – Silicates
1. Silicates
– Tetrahedron
• fundamental
building block
• 4 oxygen ions
surrounding a
much smaller
silicon ion
Silicon-oxygen
tetrahedron
(SiO4)4-
Mineral Groups – Silicates
•
Joining Silicate Structures
– How tetrahedra may be linked:
• independent tetrahedra
• single chains
• double chains
• sheets
• 3-D framework
Mineral Groups
– Silicates –
Mineral Groups – Silicates
Olivine Group
dark silicates (Fe-Mg)  ferromagnesian
No cleavage
Mineral Groups – Silicates
Pyroxene Group
Ferromagnesian / dark silicates (Fe-Mg)
Augite
2-directions
of cleavage
(at nearly 90 degrees)
Mineral Groups – Silicates
Amphibole Group
Ferromagnesian / dark silicates (Ca, Fe-Mg)
Hornblende
2-directions
of cleavage
(not at 90 degrees)
Mineral Groups – Silicates
Mica Group and Clay Minerals
light silicates (K, Al)  non-ferromagnesian
Muscovite
1-direction
of cleavage
Mineral Groups – Silicates
Feldspar Group
K-feldspar
light silicates (K-Na-Ca, Al)
Most common mineral group
Orthoclase
Plagioclase
2-directions
of cleavage
(at 90 degrees)
Ca/Na-feldspar
Mineral Groups – Silicates
Quartz
light silicates (pure SiO2)
no cleavage
(conchoidal fracture)
hard, resistant to weathering
Quartz
Minerals
Mineral Groups
2. Carbonates
• Minerals that contain the elements carbon,
oxygen, and one or more other metallic
elements
3. Oxides
• Minerals that contain oxygen and one or more
other elements, which are usually metals
Minerals
Mineral Groups
4. Sulfates and Sulfides
• Minerals that contain the element sulfur
5. Halides
• Minerals that contain a halogen ion plus one or
more other elements
6. Native elements
• Minerals that exist in relatively pure form
Sulfides
Native Copper