Transcript Rocks and Minerals 1 Minerals

What is a Mineral?
• A mineral is a:
– Naturally occurring,
– Inorganic,
– Crystalline solid,
– That has a definite chemical
composition.
Some Minerals
What is a Rock?
• A rock is a:
– Naturally formed,
– Consolidated material,
– Composed of grains of one or
more minerals.
Some Rocks
Mineral Characteristics
• Minerals are classified based
on their physical properties
and chemical properties.
How Do We Identify Minerals?
• We identify minerals using physical
properties of:
– Color and streak
– Luster
– Hardness
– Cleavage
– Fracture
Color and Streak
• Color is the first thing that most people
notice about minerals.
– Color is a useful property but many
minerals are found in a variety of colors.
• Streak is the pulverized color of a mineral.
– Streak is determined by scraping the
sample across a porcelain plate.
Luster
• Luster is the quality and intensity of the
light that is reflected from the surface of
a mineral.
• Luster is described as metallic or nonmetallic.
– Non-metallic is more common, most
importantly is glassy.
– Earthy luster is uncommon but appears
silky, or pearly.
Earthy and Metallic Luster
Hardness
• Hardness is a minerals resistance to
being scratched, or the
“scratchability” of a mineral.
– In order for a mineral to scratch another
it must be harder.
– Frederich Mohs made up a scale, called
the Mohs Scale, to compare hardness.
Cleavage
• Cleavage is the tendency of a mineral
to break along one or more smooth,
flat, lustrous surfaces.
– Cleavage is described as perfect, good,
or poor.
– Different minerals have different planes
of cleavage.
• Examples: mica has one perfect plane,
halite has three perfect planes
Fracture
• Fracture is the way a mineral breaks
other than cleaving.
– Fracture is an irregular break pattern
– Fracture can be described as uneven,
conchoidal (shell-like), splintery, earthy
(like clay)
Formation of Minerals
All minerals are crystalline, ,made of atoms
arranged in a pattern.
Crystals are minerals with geometric
shapes and smooth flat surfaces called
faces.
Each kind of mineral has its own crystal
shape and will develop into this form if it
has room to grow w/o restrictions.
Various Crystals
6 Basic Crystal Systems
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Cubic
Hexagonal
Orthorhombic
Monoclinic
Tetragonal
Triclinic
Chemical Composition
• All minerals are made of elements and
some minerals can be identified by their
special chemical composition.
• Some minerals are made up of only one
element (such as gold, copper, sulfur).
• Most minerals are made of compounds,
two or more elements chemically
combined.
Chemical Composition Silicates
• Silicates are the most common
minerals and are combinations of silicon
and oxygen with other elements.
• Examples are quartz, feldspar, mica and
hornblende.
Silicates
Chemical Composition Carbonates
• Carbonates are minerals which are
compounds of 1 carbon atom and 3
oxygen atoms.
• Examples are calcite and dolomite.
Carbonates
Calcite
Dolomite
Calcite Color Varieties
Chemical Composition –
Oxides and Sulfides
• In an oxide, the mineral iron
combines with oxygen.
– Example is magnetite
• In a sulfide, the mineral iron
combines with sulfur.
– Example is pyrite (fool’s gold)
Oxides and Sulfides
Magnetite (Lodestone) and Pyrite (Fool’s Gold)
Structure of Minerals
• Structure refers to the arrangement
of the atoms in a mineral.
• Silicon and oxygen, the most
common elements in the Earth’s
crust, combine chemically to form a
structural unit in the shape of a
tetrahedron (a four-sided solid
triangle)