Geology 1100/Dynamic Earth
• GEOLOGY is the study of everything on this Earth. Geo = earth, ology = study of. Rocks, glaciers, volcanoes, mountain building, etc –all of these are covered by geologists.
• What types of things do geologists study?
▪ What is a Rock? Slide: the left picture is a rock and the right picture is a mineral. ▪ Rocksare a collection or aggregate of minerals. Three or more minerals makes a rock.
▪ In order to be a mineral, you have to meet 5 criteria:
1. Solid - Can not be a liquid
2. Inorganic - Not living
3. Natural -You were made by the natural processes that happen on earth.
Even if something is made in the lab, it is mimicking the natural
processes that happen on earth.
4. Specific chemical composition - Things like H20, NaCl – there’s nowhere
you can go that H20 won’t be H20 Don't forget about the age old question of write an expression that evaluates to true if the value of the integer variable widthofbox is not divisible by the value of the integer variable widthofbook. assume that widthofbook is not zero. ("not divisible" means has a remainder.)
We also discuss several other topics like vphy uga
5. Crystal-like patterns or structures – Salt forms cubes because when an
Na bonds to a Cl it will form in a certain pattern creating a specific
crystal-like structure. It will always look the same way
▪ There are over 4000 officially named minerals.We also discuss several other topics like thanatos and libido
▪ Examples of minerals are included in Professor Hawkins’s slides: Muscovite and Biotite. The mineral muscovite is all over Auburn. It’s solid, not living, natural, there is a set chemical composition (KAl2Si3O10OH2) and has a set crystal-like structure. Muscovite has aluminum and Biotite has magnesium. Little things can be changed up to completely alter a mineral.
Don't forget about the age old question of fau math day
▪ Ice is a mineral because it meets the 5 criteria. It is solid, it is inorganic, it is natural, it has a specific chemical composition (H20) and it does indeed form a crystal-like structure. There are 14 different varieties of ice. Don't forget about the age old question of bio 123
1. Temperature and Pressure are two key factors that influence crystal structure. Temperature and pressure is what #5 of the mineral criteria is dependent on.
▪ Most minerals are composed of the following 8 elements:
1. Silicon (Si)
2. Oxygen (O)
3. Aluminum (Al)
4. Magnesium (Mg)
5. Iron (Fe)
6. Sodium (Na)
7. Potassium (K)
8. Calcium (Ca) We also discuss several other topics like charlie mitchell uf
▪ SILICATE MINERALS are formed by the bonding of silicon and oxygen at extremely high temperatures. Silicates are formed in magma.
1. Silicates make a tetrahedral. It is composed of 1 silica atom and 4 oxygen atoms. THE OVERALL CHARGE OF THE SILICA TETRAHEDRAL IS -4.
2. Because the overall charge of the tetrahedral is negative, other elements must be added and substituted to satisfy the negative charge.
o Some of these elements that could be added or substituted are the following: **KNOW THE NUMBERS**
▪ FE +2
▪ MG +2
▪ AL +3
▪ K +1
▪ NA +1
▪ CA +2
▪ SI +4
▪ O -2
▪ BOWENS REACTION SERIES – REFER TO CHART IN ORANGE BOOKLET
1. Silicates are formed in magma. As the magma cools, there will be less energy in the system and the bonds will become stable. When the bonds become stable we make minerals at HIGH TEMPERATURES.
2. By adding some Fe or Mg to the tetrahedral structure OLIVINE is made. 3. Once olivine is made, the magma will continue to cool. The individual
SiO4 tetrahedral will start to bond together. This is caused by the temperature decreasing. A lower temperature leads to lower energy which in turn causes more bonding to occur.
4. Single chains are formed creating a different mineral (PYROXENE) because there is now a different structure.
5. As the temperature continues to cool, double chains are formed, again creating a different mineral (AMPHIBOLE) because the structure has changed.
6. The cooler the temperature, the more bonding occurs creating lastly a sheet structure (BIOTITE).
7. As we work our way down the list, Fe and Mg become less abundant. Al will start to come into play. Since Al has a +3 valence number, it will allow for further substitution. Aluminum contributes to forming
▪ There are two main groups of minerals:
1. SILICATES = most minerals within the Earth’s crust, otherwise known as “rock forming” minerals. They are composed of cations bonded to
groupings of silicon and oxygen atoms.
2. NON-SILICATES = all other minerals; not “rock forming” minerals.
▪ IONIC SUBSTITUTION is defined as ions with similar charges and sizes that freely substitute in a crystal structure.
o There are six classes of nonsilicate minerals
▪ OXIDES are consisted of various cations bonded to oxygen
1. Examples include
o corundum (AL203), sapphire and ruby
o hematite Fe203 (dirt roads)
o Red Mountain, Birmingham (iron ore)
2. Oxides are what are known for rusting.
o When free oxygen interacts rusting occurs
▪ SULFIDES are consisted of cations bonded to sulfur generally (S-2) 1. Examples include
o PYRITE or “fools gold” - consists of iron bound with sulfur. We
don’t like this because it is worthless
o GALENA consists of lead and sulfur
o SPHALERITE – if you put acid on it, it will bubble and smell bad!
▪ CARBONATES consist of cations bonded to “carbonate ionic group” or “carbonate radical” (CO3)
1. Examples include
o Aspirin or tums. The outer white chalky coating is made of
carbonates (CALCITE & DOLOMITE). Carbonates are able to be
digested in the human body so medicine is incorporated into
▪ SULFATES consist of cations bonded to the “sulfate ionic group” (SO4) 1. An example is GYPSUM that makes up sheet rock used for walls in houses.
▪ HALIDES arecations bonded to: F-1, Cl-1, or (OH)-1
1. Examples include
o Fluoride, chloride & hydroxide
o FLUORITE & HALITE are both halides and are distinguished by
being salty to the taste.
▪ PHOSPHATES are cations bonded to the “phosphate ionic group” (PO4) 1. Examples include
o APATITE – Ca5(PO4)3(F, Cl, OH)
▪ Fluoride helps keep your teeth strong
▪ Cloride has soft and fuzzy characteristics
▪ Hydroxide isn’t as strong as the fluoride but is similar
o Mineral Properties
▪ LUSTER describes the appearance of reflected light from the mineral’s surface. Luster can be described as
3. Dull/earthy OR non-metallic
▪ HARDNESS – photo borrowed from
▪ CLEAVAGE/FRACTURE – if a mineral breaks along straight planes it is said to
have good cleavage. Weak bonding yields planer cleavage. Because of weak bonds, mica splits easily between “sandwiches.”
1. IF A MINERAL HAS BASAL CLEAVAGE, THAT MEANS THERE IS ONLY ONE CLEAVAGE PLANE. THIS IS WHY MICA CAN BE SPLIT INTO SHEETS. EXAMPLES OF BASAL CLEAVAGE ARE MUSCOVITE AND BIOTITE **LAB MIDTERM QUESTION**
2. A CONCHOIDAL FRACTURE in glass appears rounded or scalloped and is said to have bad cleavage.
▪ HABIT or CRYSTAL FORM shows how the crystal will grow if there is room 1. Quartz has certain interfacial angles so no matter where you grow it, it will grow into a certain type of structure (won’t be tested on that but is a good example).
2. Feldspar is very rare to run into
3. Chrysotile Asbestos (like you would find behind the walls in an old house) – the minerals are stretched like cotton candy. It’s best to just leave it alone. Once you mess with it, the particles get into the air and inhaling those particles is what is dangerous about asbestos.
▪ COLOR is obvious feature but is unreliable to use to determine the type of mineral. It has to do with the way light bounces off the object.
1. Color can be diagnostic for the trace element. Si02 – All of the following examples are different colors but they are still examples of the mineral Quartz. That’s why color is misleading when identifying.
o Quartz is usually clear with no impurities
o Rose quartz (Ti) contains natural titanium which makes it appear pink
o Smoky quartz appears darker because of radiation factors U, K, Th
o Amethyst contains Manganese (Mn)
o Milky quartz has fluid inclusions or “bubbles” in the crystals
which make it appear white.
▪ STREAK is the color of a mineral in it’s powdered form. A streak is obtained by rubbing the mineral against an unglazed porcelain plate. It is less variable than color and useful for distinguishing between minerals with a metallic luster.
▪ STRIATIONS are found on plagioclase feldspar. They appear as straight and parallel lines.
▪ MAGNETISM is apparent in the mineral Hematite (Fe2o3)
▪ DOUBLE REFRACTION appears in calcite crystals. The light is split into two components. Some minerals will respond to a black light. Calcite crystals react with acid.
▪ DENSITY = mass/volume
▪ SPECIFIC GRAVITY is not something we will study in depth but it’s the ratio of the substance’s mass to the mass of an equal volume of water.
o Two broad categories of color and density are FERROMAGNESIAN and NONFERROMAGNESIAN SILICATES meaning they are either iron and magnesian bearing or not. The presence or absence of Fe and Mg strongly affects the color and density of the minerals.
▪ FERROMAGNESIAN SILICATES (CONTAINING FE AND MG) are dark in color and range in density from 3.2-3.6 g/cc. Examples include
1. OLIVINE– comprises over 50% of the upper mantle of the earth
▪ NONFERROMAGNESIAN SILICATES (NOT CONTAINING FE AND MG) are lighter in color and their density is close to 2.7 g/cc.Examples include
3. QUARTZ –a major component in sedimentary rocks
• The Rock Cycleis how all rocks on earth relate and are interconnected.
o There are three types of rocks: IGNEOUS, SEDIMENTARY AND METAMORPHIC ▪ IGNEOUS are generated from the crystallization of magma or lava.
1. Magma is intrusive and lava is extrusive.
o MAGMA has the elements that are important for building
minerals. Some of the common elements are the following
▪ O, Si, Al, Fe, Mg, K, Na, Ca
2. The crystallization pathway (BOWENS REACTION SERIES) predicts the
types of minerals and in what order they will crystallize.
o Crystallization can occur within the Earths surface (INTRUSIVE) or
on the surface (EXTRUSIVE).
▪ Intrusive rocks will cool at different rates depending on
their depth within the earth. When rocks cool SLOWLY
they have time to grow LARGE CRYSTALS and that
generates a specific type of TEXTURE.
3. ANY TIME MAGMA OR LAVA IS CRYSTALLIZED, IT BECOMES AN IGENOUS ROCK **TEST QUESTION**
▪ INTRUSIVE ROCK TEXTURES
1. PHANERITIC - When rocks cool SLOWLY they have time to grow LARGE CRYSTALS and that generates a specific type of TEXTURE. YOU CAN SEE THESE SAME SIZE CRYSTALS WITH THE NAKED EYE. These rock textures are formed deep inside the earth.
2. APHANITIC –Formed when rocks cool so FAST that the crystals do not have time to grow large and you have a FINE GRAINED texture. This happens when magma intrudes closer to the surface/not as deep as phaneritic. You can’t see the individual crystals on aphanitic rocks.
3. PORPHYRITIC is a mix of textures. When there is a MIXING OF COOLING RATES you will have a combination of phaneritic and aphanitic resulting in a porphyritic texture. A lot of times these rocks were probably involved in a volcanic system. That makes sense because these rocks started the
cooling process deep into the earth but as the process went on, they rose higher to the surface. You will see some big and some little crystals when looking at a porphyritic rock.
▪ EXTRUSIVE ROCK TEXTURES can also be called pyroclastics or volcanics.
1. GLASSY textures form when the lava (remember these are extrusive rocks so we’re talking about lava now, not magma) is ejected from a volcano and cools EXTREMEMLY RAPIDLY. The cooling process occurs so fast that the CRYSTAL LATTICE DOES NOT FORM PROPERLY.
o An example of a glassy texture is OBSIDIAN. Obsidian is found near volcanoes for obvious reasons.
2. VESICULAR textures are formed when the cooling process is fast, but in this case, the PRESSURE on the lava/magma has dropped so quickly, that the gases are expanding and escaping as the rock is cooling (think about shaking up a coke).
o Vesicular textures can be light and dark. The light onesare more felsic and are called PUMICE. The dark ones are more mafic and are called SCORIA.
o Pumice will float because of the little holes all over it.
3. PYROCLASTIC textures are generated from smaller pieces of rock that were blasted FROM A VOLCANO and were WELDED TOGETHER. NOT FORMED BY COOLING.
o An example of a pyroclastic rock is Tuff.
▪ MAGMA forms in the lower crust and mantle in which high temperature melts the rock and makes it into molten magma. Rock composition, pressure and water content all influence the melting temperature of rocks also. When magma reaches the surface through a volcanic eruption, it is referred to as lava.
1. If something has a high VISCOSITY it is considered to resist flow. The
higher the viscosity, the thicker something is. Think about iHop syrups.
The blueberry syrup that has been sitting on the table for days and is
cool is going to have a higher viscosity than the piping hot maple syrup
that the waitress brings out with your pancakes. Temperature is the
deciding factor for how viscous something is. SILICA in magma causes it
to be more viscous.
2. High viscosity = thick and stiff Low viscosity = thin and “runny”
o The following chart is a necessary key to determining different types of INTRUSIVE rocks based on their appearance. THIS IS SO IMPORTANT!!!!
▪ FINE GRAIN = APHANITIC COARSE GRAIN = PHANERITIC
▪ FELSIC = NONFERROMAGNESIAN (no Fe and Mg)
MAFIC = FERROMAGNESIAN (has Fe and Mg)
▪ The more SILICA, the higher the viscosity. The lower the amount of SILICA the lower the viscosity (more runny).
▪ RYOLITE AND GRANITE HAVE THE SAME MINERALS JUST A DIFFERENT TEXTURE. The same goes for ANDESITE and DIORITE as well as BASALT and GABBRO.
• Intrusive Rock Bodies: when magma cools in the earth, it forms an intrusive body. o INTRUSIVE ROCKS exist in bodies or structures that penetrate or cut through pre-existing country rock (country rock refers to rock that was already there).
o INTRUSIVE BODIES are named based on their size, shapeand relationship to country rock.
▪ DEEP INTRUSIONS are called PLUTONS
1. Plutons form at considerable depth beneath the surface when rising
blobs of magma (aka diapirs) get trapped in the crust.
2. They CRYSTALLIZE SLOWLY in warm rock.
3. They are generally composed of COARSE-GRAINED ROCKS.
4. They are PHANARITIC in texture.
▪ INTRUSIVE IGNEOUS BODIES
1. VOLCANIC NECK (porphoritic): shallow intrusion formed when magma
solidifies in the throat of a volcano
o Examples include Edinburgh, Scotland (under the castle the
base is a volcanic neck). Devil’s Tower is also a volcanic neck.
2. DIKE (aphanitic): tabular intrusive structure that cuts across any layering in country rock CUTS ACROSS
o Dikes have a low viscosity.
o Examples include Ship Rock, New Mexico and La Veta,
o Large fins that are seen near volcanoes are considered dikes. 3. SILL: tabular intrusive structure that PARALLELS layering in country rock FILLS in horizontally. Sills can be quite large.
o An example is the Palisades Sill in New Mexico
4. PLUTON (BATHOLLITHS and LACCOLITHS): large, blob-shaped intrusive body formed of coarse-grained igneous rock, commonly granitic. o BATHOLITHS - Large plutons (exposed over >100 km2).
▪ Examples include Mount Rushmore in the Black Hills of
South Dakota (granite) 1.6 billion years old.
o LACCOLITHS –exposure is less than 100 km2. Laccoliths are a baby version of Batholiths.
▪ SHALLOW INTRUSIONS are called DIKES and SILLS
1. They form <2 km beneath Earth’s surface.
2. They solidify FAIRLY QUICKLY in cool country rock.
3. They are generally composed of FINE-GRAINED rocks.
4. They are APHANITIC in texture.
▪ COLUMNAR JOINTING occurs when lava or magma cools and contracts quickly enough to cause jointing. Most columns tend to have 5 or 6 sides but have as few as 3 and as many as 7 sides. There a lots in Iceland. When contraction occurs at centers which are equally spaced, a hexagonal fracture pattern will develop.
▪ A XENOLITH is a rock fragment that becomes enveloped in a larger rock during the crystallization of the encapsulating rock. Magma melts around a xenolith. The xenolith is mafic and requires higher temperatures to melt so that’s why it’s visible inside the younger rock that melted around it.
1. Felsic things melt at lower temperatures (the rock surrounding the xenolith).