MINERALS
• What is a mineral?
• How do we differentiate a mineral
from a piece of wood or a human?
• What is a rock?
Minerals
• What is a mineral?

Naturally occurring (not man-made)

Inorganic


Crystalline Solid (interlocked pattern of
molecules)
Definite chemical structure which give
it unique physical properties.
Ex. Diamonds
Minerals vs. Rocks
• There are nearly 4000 known minerals but most rocks are formed by only a few
dozen minerals.
• Rocks are aggregates (mixtures) of
minerals. So . . . minerals are the building
blocks of rocks.
• Question :
How do minerals come together to form a
rock?
Composition and Structure of
Minerals
• To understand how minerals form, we need
to understand the characteristics of
elements and atoms.


Elements are the basic building blocks of
minerals. There are over 100 known
elements.
Atoms are the smallest particle of
matter that exhibits all the
characteristics of an element.
Composition and Structure of
Minerals

Atoms are made up of:
 Nucleus, which contains



Protons- positive electrical charges
Neutrons - no charge
Shells which surround the nucleus and
contain Electrons - negative electrical
charges
• The mass (density) of an element depends on the
number of protons and neutrons in the nucleus.
Combining Elements to Form
Minerals



Elements combine with each other to
form a wide variety of minerals.
The new mineral (compound) will have
very different physical properties from
the elements that combined to form it.
Ex: 1 Calcium
1 Carbon
3 Oxygen
CaCO3
Combining Elements to Form
Minerals



Since rocks are mixtures (not chemical
combinations) of minerals, minerals
keep their physical properties within a
rock.
Question: Is it possible for two
different minerals to have the same
chemical composition?
YES! Both diamond and graphite are
made of carbon. The difference
between these two minerals is the way
in which the carbon atoms are arranged.
Rock Forming Minerals
• The most common rock forming minerals
are composed of 8 elements:







Oxygen (O)
Silicon (Si)
Aluminum (Al)
Calcium (Ca)
Sodium (Na)
Potassium (K)
Iron (Fe) and Magnesium (Mg)
• There are just a few dozen minerals that
we call the rock-forming minerals.
Silicate Minerals
• Silicate minerals:

Contain both silicon (Si) and oxygen (O)

The most common rock-forming minerals

May contain one or more other elements
• Silicates make up 96% of the Earth’s crust.
Silicate Mineral Groups
• Feldspars –
form depending on which metal
combines with the Si + O atoms

Two common types of feldspars:

Orthoclase (K, Al)

Plagioclase (Ca, Na)

Most plentiful mineral group
• Quartz –
composed ONLY of Si + O atoms
( NO other elements )
Silicate Minerals
Non-Silicate Minerals
• Major groups: *Contain no Silicon


Oxides (metal + O) Ex. Hematite, magnetite
Sulfides (metal + S) Ex. Pyrite “fool’s gold,”
galena

Sulfates (S +O) Ex. Gypsum [plaster]

Halides Ex. Halites [salt]


"Native" elements (don’t combine with any other
elements) Ex. Gold, silver, carbon, copper
Carbonates (C + O) Ex. limestone, marble
Non-Silicates make up 4% of the Earth’s crust.
Non-Silicate Minerals
Non-Silicate Minerals
Mineral Properties
• Minerals have lots of different properties
that help us identify them:









Crystal form -set of faces that have a definite
geometric relationship to one another.
Luster –metallic or nonmetallic shine
Color
Streak –mineral’s color in powdered form
Hardness –Mohs hardness scale/scratch
resistance of one mineral against another
Cleavage –how it breaks along preferred planes
Fracture –no preferred plane (no flat surface)
Specific gravity -describes the density of the
mineral
Taste, Smell, Fluorescence etc.
Identifying Minerals
• Color – can help with
mineral identification.
• Color of the mineral
• Color of the streak on
a porcelain plate
• Example = Hematite is
gray in color and has a
red streak
Identifying Minerals
• Luster – shiny or dull
• Luster - the way a
mineral reflects light
• Look for luster on a
fresh surface.
• The three major types of
luster are



metallic,
glassy (vitreous)
and dull.
Plane
Cleavage – how mineral breaks
Name
1
=Basal
2
=Prismatic
3
=Cubic
3
=Rhombohedral
(a) cubic (b) 12-sided (c) octahedral (d) hexagonal
Identifying Minerals
• Most minerals (except metals) have one or more
cleavage planes that also help in determining their
identity.
• Cleavage Plane – A region where a rock cleanly
splits
• Occur in areas of weak bonds between atoms and
molecules.
• Mica has 1 cleavage plane
• Halite has 3 cleavage planes
Mohs hardness scale
1. Talc
7. Quartz
2. Gypsum/fingernail
8. Topaz
3. Calcite/penny
9. Corundum
4. Fluorite
10. Diamond
5. Apatite
6. Potassium Feldspar/steel nail
Scratch one mineral against another to see how
resistant it is.
Material
Mohs hardness scale
Streak plate
~7
Glass plate
5.5 - 6
Nail
~4
Copper/Penny
~3
Fingernail
~2
Mineral Identification
• Common items to test for hardness
• A fingernail (2.5) will scratch gypsum and
be scratched by calcite
• A penny (3) is scratched by fluorite
• Glass (5.5- 6) scratches apatite and is
scratched by orthoclase (a feldspar)