Notes Unit 1:
made from elements. Elements are substances that cannot be broken
down by normal chemical means. All elements are listed in the
Periodic Table of Elements. Some common elements in minerals are
Oxygen (O), Silicon (Si), Calcium (Ca) and Sodium (Na).
NOVA Video on Minerals
Brief Introduction to Minerals
All minerals have four properties:
1. All minerals are naturally occurring
2. All minerals are inorganic (that means non-living)
3. A different chemical formula can be written
for each mineral and that formula is constant for that mineral.
ex. Galena is PbS- it has one lead
atom (Pb) and one sulfur (S) atom in each molecule.
4. Most minerals have an unique crystalline
shape given the right growing conditions (as in a cave).
Minerals have many different properties, and
geologists use these properties to determine what kind of mineral
is before them. Scientists use a combination of properties to
distinguish between these minerals, using the process of elimination.
Video on Identifying Minerals
The following is a description of
each of these properties:
Color is usually the first property observed
when handling a specimen. Color alone is not reliable, but it
can help us to eliminate possibilities. We must be sure we have
a freshly exposed surface, because weathering can change the color
of a mineral. Some minerals, such as sulfur, always have the same
color (yellow). Other minerals may have different colors. One example
is quartz, which may be clear, purple, pink and even gray!
Luster is the way light reflects from a mineral's
surface. Luster is either metallic or nonmetallic. Metallic minerals
look like.... well, a metal. Nonmetallic minerals can be glassy,
dull, brilliant, waxy, earthy, or pearly.
The color of the powder of a mineral when scraped
on a porcelain plate. Oddly sometimes the powder of a mineral
can be different from color of the mineral itself. Pyrite (fool's
gold) is gold in color, but its streak color is dark gray or black!
Hardness is a mineral' s ability to resist
being scratched. Talc, the softest mineral, can easily be scratched
with a finger nail. Diamond is so hard that it can't be scratched
by another mineral. Hardness does not describe a substance's ability
to resist being broken. Even though diamond is the hardest mineral,
it can be broken if you smash it with a hammer. To show the hardness
of mineral, we use:
Moh's Scale of Hardness.
Talc- 1 Softest
Diamond- 10 Hardest
To determine the hardness of a mineral, scratch
it with these minerals, and find out which minerals will and won't
scratch it, and you know that mineral's hardness falls between
those minerals. For instance, if a mineral is not scratched by
Quartz, but is scratched by Topaz, the hardness must be between
7 and 8. Get it?
Cleavage is the
tendency of a mineral to break parallel to atomic planes in its
crystalline structure. Perhaps the best example of cleavage is
Muscovite mica, which is a mineral that breaks in parallel sheets.
Mica always flakes off in thin sheets, like pieces of paper off
of a giant stack of papers. Its atoms line up in sheets, and this
is what provides a plane of weakness. Another example is Halite,
that has cleavage in three directions at angles of 90 degrees
from each other. When a piece of Halite is broken, it breaks into
many smaller cubes.
Fracture is when
a mineral breaks into jagged edges. Some minerals have no planes
of weakness, so they have no cleavage.
Some minerals have a distinct fracture. Quartz is a perfect example. Obsidian
always fractures in a pattern that looks like a clam shell. Obsidian
is also called volcanic glass.
Crystal Shape is the natural geometric shape of a mineral. Minerals grow into
different shapes because the internal arrangment of their atoms form unique patterns. Each
layer is built up much like layers of chocolate would on an ice
cream cone dipped again and again into melted chocolate sauce. Minerals must have time to grow slowly.
ex. Quartz crystals form hexagonal shapes,
salt, diamonds and pyrite are cubic, and mica is monoclinic.
5. Other Properties-
Some minerals have special properties.
such as magnetite, give a magnetic tug when close to magnets.
In fact, early compasses where made by floating magnetite on a
piece of wood in water.
glow under UV (black) light. Some of the colors
are amazing! ex. Calcite
Radioactivity- some minerals emit radiation such as uraninite which contains uranium.
Double refraction is a dead give away property of Iceland spar calcite. When
this mineral is placed on paper you see double!
Reaction to Acid- HCl, or hydrochloric acid, can be used to identify calcite or limestone. Calcium Carbonate bubbles furiously when acid is applied.
is tested by using your sense of taste. If you lick it,
it tastes very salty, because salt is actually made from Halite.
Minerals are the building blocks of rocks. Nearly one hundred of the thousands of known minerals
make up ninety five percent of the earth's rocks. Twenty of these
minerals are most likely to be found in rocks found in the field.
The rock cycle is the constant changing of rocks from one form to another. Any rock type can form from any other rock type.
Rock Cycle Reference Table video
Bill Nye on Rocks video
Untamed Science on Rock types video
Igneous rocks form by the crystallization of
lava, molten rock cooling on the surface of the earth or magma, molten material solidifing inside the earth.
Extrusive Volcanic Rock
Formed when molten (liquid) rock called lava hardens quickly on the Earth's surface.
Biggest Volcanic Eruptions video
Really fast cooling lava does not give crystals time to grow and form. So the rock formed has a glassy texture.
If the lava cooled a little more slowly, crystals will form but they are still invisble to the eye. You would need a magnifying glass to see them.
If the lava had air pockets in it it would harden with a bubbly texture called Vesicular Texture.
ex. Scoria and Pahoehoe
Intrusive Plutonic Rock
Formed when molten rock hardens slowly deep inside the earth.
The more time a crystal has to form, the larger the crystal will be.
If given a long enough time to cool, crystals
can get really big! Magma that is stuck underground will cool very slowly, because
it is insulated by the surrounding rock. So for hundreds of years, crystals can grow to 12 meters and more. Some magma chambers cool only a few degrees per
Mexico's Giant Crystal video
The intrusive igneous rocks you'll see in class will be around 1 inch sized crystals that interlock together like puzzle pieces.
ex. Granite and Gabbro
Igneous rocks are identified based on their
texture and mineral composition.
Texture is the size of mineral crystals.
Mineral composition is
simply the minerals that make up an igneous rock.
Felsic or light colored igneous rocks, like granite, are listed in your reference
table as having lots of quartz and feldspar in it. Mafic or dark rocks like basalt is heavy in density and made of proxene and
Igneous Rocks and the Reference Tables video
bits of rock) are formed by the weathering of rocks by wind,
water, or ice. Most sediments are rock, but some can be pieces
of plants or animals. When
these materials are deposited, they form loose layers which then gets cemented into solid rock layers.
Bill Nye on Sedimentary Rocks
Photos of Sedimentary Rocks
Types of Sedimentary Rock
Clastic- Made of sediments
held together by compaction and cementation (rock glue).
In order of increasing size, common clastic rocks include Shale, Siltstone, Sandstone and Conglomerate (or Breccia).
The more rounded the sediments making up the rock, the more it has tumbled in a stream.
Chemical or Crystalline-
Forms when mineral grains precipitate out of solution by water evaporating.
Ex. Rock Salt or Gypsom
Organic or Bioclastic- Animal
or plant remains make up compacted and altered rock.
Coal is made of squashed plants
and Fossil Limestone is formed when animal skeletons sink to the
bottom of the sea and collect. In New York they found two mastodon skeletons in 2000!
Sedimentary Rock Video
Sedimentary GeoScience Video
Classification of Sedimentary Rocks
Most sedimentary rocks are formed by deposition
of sediment in shallow seas, oceans and lakes. They are laid down in flat
layers (a great identifying feature) and sometimes contain fossils.
The clastic sedimentary rocks are classified by grain size.
Sedimentary Rocks and the Reference Tables
Identifying Sedimentary Rocks
Metamorphic rocks are formed by changing sedimentary, igneous or metamorphic rock. Heat and pressure can cause the formation
of metamorphic rocks through contact
with magma and/or deep burial.
Most minerals expand when heated, causing atoms
to move apart, stretching the bonds that hold them together. If
heated enough, the bonds will break, and the mineral melts. In
a metamorphic rock, some bonds break, but not all, so some changes take place but the rock does NOT melt. Metamorphic rocks have a different set of characteristics than
its original form. One example is limestone. When it is "baked"
by the contact with magma, it turns into marble.
Pressure has the opposite effect of heat. It
pushes the atoms within rocks together. This pressure will result in some sort
of deformation. Often, rocks seem to have bands that are twisted and turned, resulting from metamorphosis of sedimentary rocks.
Good ways to identify a metamorphic
rock include layers of flattened crystals, distorted structure and
the appearance of exotic crystals.
Metamorphic Rocks and the Reference Table
Metamorphic Rock Video
Characteristics of Metamorphic Rocks
Change to Crystalline Texture-
During metamorphosis, the size, spacing, and
shape of the grains are changed. They may fuse due to heating
and create brand new, large crystals. In New Hampshire they found
a single crystal of Beryl had grown to be 250 feet long! Garnet
schist is a good example of a rock that grew bizarre crystals
with help from metamorphosis.
Pressure which forces the grains closer together
can cause the volume to decrease, while the mass remains the same.
The density of the rock increases.
Foliation and Banding-
Sometimes, heat and pressure can produce a
thin layer of flattened crystals aligned on the same plane called foliation. Foliation can be extreme when minerals
recrystallize and separate out according to density, like oil
and water. For example gneiss has has wavy stripes of black and white crystals. Extreme foliation is called banding.
Distortion of Layers-
When a sedimentary rock is metamorphosed, its
layers become distorted (that means the layers are wavy).
Rock Cycle Rap- Mr. Lee
The Rock Cycle Rap- Mr. Beasley
The Rock Cycle Song