Rock Unit
Basic Chemistry
I. Matter
A. Matter - anything that has mass and volume. Everything in the
universe is made of matter.
B. Matter is made of atoms, which are the smallest part of an
element that still has that element's properties.
C. Elements are substances that cannot be changed into simpler
substances by chemical reactions.
D. Atomic structure:
1. The nucleus contains (+) charged protons and neutral (0)
charged neutrons, which make up more than 99.9% of an
atom's mass.
2. Much smaller, negatively (-) charged electrons orbit the
nucleus much as the planets orbit the sun in the solar
system.
3. The nucleus is tiny, so most of an atom is empty space!!
4. There is a good diagram of an atom's structure on page 30
of the text.
E. Atomic number = the number of protons in an atom's nucleus. It
is this number that dictates what element an atom is.
F. Mass number - the number of protons and neutrons in an atom's
nucleus. This number is usually larger than the atomic number.
G. Number of neutrons = mass number - atomic number.
H. Isotopes are different forms of the same element. They only
differ in the number of neutrons in the atom's nucleus. The
number of protons remains the same.
I. Several elements can combine to form compounds, which are
substances composed of two or more elements. The smallest
chunk of a compound is a molecule.
II. The Chemistry of Minerals
A. Note the 5 requirements that define minerals on page 34 of the
textbook.
1. Minerals occur naturally
2. Minerals are solids
3. Minerals ave definite chemical compositions (that is,
elements in definite chemical proportions).
4. Minerals have atoms arranged in an orderly pattern
5. Minerals are inorganic (not formed by plant or animal
activities).
B. Native minerals are minerals that are made of only one kind of
element.
C. Most elements are metals, which are good conductors of heat
and electricity.
D. Non-metals are good insulators of electricity and are on the right
side of the Periodic Table.
E. Minerals can form in many ways. Probably the two main ways are
as follows:
1. The cooling of magma in underground chambers.
2. The evaporation of ancient lakes or seas.
F. Minerals form into regular shaped solids called crystals. Crystals
have smooth faces and a regular geometry to them.
G. Check out some examples of crystal shapes on page 39 of the
textbook.
H. Most minerals are silicates, which are comprised of silica
tetrahedrons. Silica tetrahedrons are made up of 1 silicon atom
bonded covalently to 4 oxygen atoms to form a tetrahedron that
is perfectly symmetrical. This is one of the most abundant
molecules in the Earth's crust!
I. Silica tetrahedrons can combine in many ways to form different
minerals. Check some of the bonding arrangements out for this
molecule on page 40 of the textbook.
How To Know Minerals
I. Identifying Minerals
A. Rock-Forming Minerals - Common minerals that make up most
rocks in the Earth's crust.
B. Mineral Identification Features:
1. Color - Easily observed. Not very reliable though.
Many minerals have similar colors.
2. Luster - How shiny the mineral is. Many descriptive terms for this
characteristic (luster vs. non-luster or Metallic vs. Non-Metallic)
3. Crystal Shape - Shape of crystal is characteristic to many
minerals.
4. Streak Tests - What color is the streak left behind by a
mineral after it is rubbed on a rough white tile?
Colors are sometimes unique.
5. Cleavage - Tendency to split along flat surfaces.
6. Fracture - What does the mineral look like after breaking
along a non-cleavage surface? Is it conchoidal - like obsidian?
7. Hardness - Mineral's resistance to scratching. Moh's scale
is used in this test. See chart on page 50 of your textbook.
C. Specific Gravity - Ratio of mineral's weight to the weight of an
equal volume of H2O. See formula below:
Specific Gravity = weight of sample in the air
loss of weight in water
D. Acid Tests - Cold, weak HCl bubbles up in the presence of calcite.
E. Some special properties of minerals:
1. Magnetism - Magnetite
2. Taste - Halite (Rock salt)
3. Double Refraction - Calcite
4. Phosphorescent - Willemite, Sphalerite
II. Rock-Forming Mineral Descriptions
A. Silicates - Most important building-block for minerals
1. Forms silica tetrahedrons, where 4 oxygen atoms bond to 1
silicon atom. Quartz is all silica tetrahedrons, with a
chemical formula of SiO2 because the oxygen atoms get
2.
3.
4.
5.
shared with neighboring silicon atoms.
Feldspars - Most abundant mineral on Earth. Has some
aluminum in it. 60% of Earth's crust!
Mica - Soft mineral. Flakes easily into thin sheets.
Amphiboles - Fairly common. Dark in color. Called
ferromagnesian silicates because they
contain both iron and magnesium. Example
is hornblende.
Pyroxines - Shorter crystals than amphiboles. Look very
similar.
B. Carbonates - contain a carbonate group (CO3-2).
1. Calcite - Most common carbonate. Can be any color.
Forms rhombehedrons.
2. Dolomite - main ingredient in marble & limestone.
C. Iron Oxides & Sulfides
1. Hematite - most common iron oxide. High in iron content.
2. Magnetite - Magnetic. (lodestone)
3. Pyrite - Fool's gold. Made of iron sulfide. Looks a bit like
gold.
I. Igneous Rocks
A. James Hutton (1795) began concept of uniformitarianism, which states that:
1. The same geologic processes have always been at work.
2. These processes formed the Earth as it is today over a long period of
time.
B. Rock (def'n) - a group of minerals bound together in some way.
C. Igneous rocks form from molten rock.
D. Molten rock is called magma.
E. Rocks that cool underground are called intrusive or plutonic rocks.
1. Distinct mineral crystals are present
F. Rocks that cool quickly are extrusive or volcanic rocks.
1. Cool quickly, so very small mineral crystals are present.
G. Magma comes in different types, ranging from
600 to 1200 degrees C :
1. Felsic magma - High in SiO2 silicates. Light in color.
Typically forms at the top of a magma chamber because of its lower
density.
Examples : Granite, quartz, orthoclase feldspar
2. Mafic magma - Low in silicates. Denser material higher in magnesium
and iron. Dark colored minerals form in this. Typically forms at the
bottom of a magma chamber. Examples : Basalt, hornblende, augite,
biotite.
H. Igneous rock textures:
1. Crystal size is dictated by the rate of cooling of the magma body. A
slower cooling rate results in larger mineral crystals being formed
in the rocks as they cool.
2. Porphyritic texture - Large crystals surrounded by fine grained rock.
The rock initially cools slowly to form some large crystals and then cools
quickly to form the fine grained rock surrounding them.
I. Common igneous rocks
1. Granite - Felsic. Coarse grained rock high in quartz,
micas, and feldspar
2. Gabbro - Mafic. Large crystals. Dark minerals dominant.
3. Rhyolite - Light colored, fine-grained igneous rock.
4. Obsidian - Cools very quickly. Forms volcanic glass.
Conchoidal fracture.
5. Pumice - Felsic lava that hardened with a lot of gases in it. Many air
bubbles in it make it possible for this mineral to float on water.
II. Sedimentary Rocks
A. 3 kinds of sediments make up sedimentary rocks:
1. Clastics - fragments of other rocks.
2. Chemical - minerals that precipitate out of a watery
solution
3. Organic - Remains of plants and animals.
B. Clastic Sedimentary Rocks
1. Fragments that make up these rocks come in many sizes and shapes.
2. Come from the erosion or weathering of pre-existing rocks on land or
underwater.
3. Sediments are cemented together with either silica, calcite, or iron
oxide.
4. Sediments running into a body of water are sorted by size primarily.
Larger particles settle out first because they're heavier. Lighter silts and
clays settle out last because of their light weight.
5. 3 types of clastic rocks:
a. Conglomerate - Large rounded pebbles and sand
grains cemented together in rough water.
b. Sandstones - Mostly grains of quartz. Many pores in it can
cause 30% of it to be air! Water can usually pass through it.
c. Shale - Tiny flakes of the mineral kaolin are cemented together.
Easily broken. Usually form from muds.
C. Chemically originated sedimentary rocks
1. Usually form when swamps, lakes, ore seas evaporate.
2. Limestone - Tiny grains of calcite cemented together.
3. Rock salt (Halite) - Table salt. Crystals form as seas
evaporate.
4. Gypsum - Form from evaporating seas as well. Main
ingredient of wallboard.
D. Organic Sedimentary Rocks
1. Mostly limestone and coal.
2. Organic limestones form from the shells of dead
microscopic organisms and the shells of ancient marine mollusks.
E. Stratification is the visible layering of many sedimentary rocks.
Gives geologists clues about how rocks had formed.
III. Metamorphic Rocks
A. Regional Metamorphism, where certain areas of the Earth's crust undergo extreme
heat and pressure form most metamorphic
rocks.
B. When shale undergoes metamorphism, it can form many new
minerals:
1. Slate - 1st rock formed when shale is metamorphosed.
2. Schists - Named for primary mineral in it. Larger crystals present.
3. Gneiss - Coarsest grained metamorphic rock. Minerals form in bands in the
rock. Usually light vs. dark
colored bands.
C. Contact metamorphism occurs when hot magma melts the rocks in contact
with it. Chemicals can react with the rocks along with the heat and pressure.
Rocks and the Rock Cycle