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
The rock cycle is the constant changing
of rocks from one form to another. Any rock type can form from
any other rock other type.
Video on Rock Cycle
Igneous rocks form by the crystallization of
molten material inside or outside the surface of the earth.
When molten rock is inside the earth it is called Magma,
and when it is outside the earth, it is called Lava. The
crystallization of igneous rocks is a complex and time consuming
process. The amount of time that a crystal has to form, the larger
the crystal will be.
If a mineral has a short amount of time to
cool, like lava that pours into water, no crystals will form,
and obsidian, or volcanic glass will be the result. If cooling takes
more time, crystals will start to form, but most often will cool
too quickly to form crystals large enough to see the crystals
without the help of a magnifying glass.
If given a long enough time to cool, crystals
will begin to form that are large enough to see with the naked
eye. Magma that is stuck underground will cool very slowly, because
it is insulated by the surrounding rock. As this material cools,
crystals will form that can be very large.
Some quartz crystals have been known to grow to a length of more
than seven feet. Some magma chambers cool only a few degrees per
Igneous rocks are identified based on their
texture and mineral composition. Texture is the size and
arrangement of mineral crystals. Mineral composition is
simply the minerals that comprise 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 on Volcanic Eruptions
bits of rock) are materials that have been transported by air,
water, or ice. Most sediments are rock, but some can be pieces
of animals or plants, and even molecules dissolved in water. When
these materials are deposited, they form loose layers , and are
then changed into rock layers.
Types of Sedimentary Rock.
Sedimentary Rock Video
are cemented (glued) together and compacted by burial. Clay sediments
make shale, sand makes sandstone and conglomerate rocks are made
Clastic sedimentary rocks can be recognized
by their layers of sediments.
or plant remains make up this rock. Coal is made of squashed plants
and Fossil Limestone is formed when animal skeletons sink to the
bottom of the sea, and collect. New York has lots of cool fossils.
In 2000 they found two mastodon skeletons!
The evaporation of water can leave behind a combination of minerals,
such as halite and other salts. Salts in a rock are not surprisingly
named- Rock Salt.
Most sedimentary rocks are formed by deposition
in shallow seas, oceans and lakes. They are laid down in flat
layers (a great identifying feature) and sometimes contain fossils.
Sedimentary Rocks and the Reference Tables
Metamorphic rocks are formed by changing either
sedimentary or igneous rocks. Many things can cause the formation
of metamorphic rocks.
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 changing takes place. Contact
with magma and deep burial can cause a rock to undergo metamorphism.
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 of rocks 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.
A good thing to look for in identifying a metamorphic
rock are layers of flattened crystals, distorted structure and
the appearance of exotic crystals.
Metamorphic Rocks and the Reference Table
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, exotic 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. Banding occurs when minerals
recrystallize and separate out according to density, like oil
and water. Gneiss is banded.
Distortion of Layers-
When a sedimentary rock is metamorphosed, its
layers become distorted (that means the layers are all wavy).