GEOL 103

S25 GEOL 103 Midterm Review: Minerals, Rocks (Igneous, Sedimentary & Metamorphic), and Geologic Structures The Basics: Mineral Naturally occurring Homogeneous Inorganic solid substance Has a definite chemical composition Characteristic crystalline structure Rock Any aggregate of minerals or materials that makes up the earth's crust. May be unconsolidated (loose) such as a sand, clay, or mud, or consolidated (solid) such as granite, limestone, or coal Minerals are the components of rocks Three types - igneous, sedimentary, metamorphic MINERALS: Classified based on a few traits that are indicative of specific minerals: Luster – the way light is reflected from a mineral. Nonmetallic Light can pass into and be reflected from within it (see- through), looks glassy, plastic, waxy, dull/earthy Metallic No light at all can penetrate the crystalline structure, so all the reflected light comes from the surface, resulting (usually) in a ‘hard’ glint or glitter, like a metal. TL;DR It doesn’t look like a metal. Streak – the color of a mineral when powdered. It can be observed by scratching the mineral on a porcelain plate, called a streak plate. Note that minerals harder than porcelain have no streak. Hardness - measure of how resistant a substance is to being scratched. We use the Mohs scale to determine the hardness (keep in mind that it is a relative scale). Some minerals have ranges of hardness instead of one singular value. How to use Mohs – if a mineral scratches the glass plate (it is harder than the glass) but leaves a streak on the streak plate (it is softer than the streak plate), that mineral has a hardness below 7 and above or equal to 5.5 on the hardness scale. ~5.5-6.5 is an acceptable range. If you cannot scratch the mineral with your fingernail (it is harder than your nail) but you can scratch it with the penny (it is softer than the penny), that mineral is between 2.5 and 3.5 Cleavage Streak plate – 7 Steel nail – 6.5 Glass - 5.5 Penny – 3.5 Fingernail -2.5 Fracture The planes along which a mineral tends to break Cleavage planes are always parallel to a crystal face Ex. Biotite has two crystal faces that are parallel meaning it has cleavage in ONE DIRECTION (basal) Any break that is not along a cleavage plane Most fracture surfaces are irregular Some will break along smooth, curved, and slightly rippled surfaces called conchoidal Ex. Quartz Other Features: Crystal faces/form - Form a mineral takes when it grows in open space (the smooth, planar surfaces that define the shape of a crystal and reflect its internal atomic structure). Cleavage occurs when mineral breaks along these planes of where bonds are weaker - that’s why the mineral split along these surfaces, and why cleavage surfaces tend to be smooth and shiny. Cleavage planes are always parallel to a crystal face, but a crystal face is not always a cleavage plane. Taste – Halite tastes salty (it has the same chemical formula as table salt) Smell – Sulfur smells like rotten eggs Reactivity – Calcite reacts with HCl acid Magnetism - Magnetite Specific Gravity - Relative weight of a mineral ex. Galena is heavy/dense IGNEOUS ROCKS: Key Concepts: Formational environments and cooling histories, Bowens Reaction Series Classified based on TWO criteria: Composition Texture For igneous rocks, the composition is associated with the COLOR. FELSIC – light colored rocks that are composed of silica and feldspar minerals that are white or pink in color (dominantly quartz and orthoclase feldspar). Note – felsic rocks can also have ~25% dark minerals as well (biotite) Can also contain plagioclase. INTERMEDIATE – rocks that are about 50% light-colored minerals (plagioclase feldspar) and 50% dark colored minerals (biotite and amphibole) MAFIC – dark colored rocks that are composed of minerals that are black in color (dominantly amphibole and pyroxene) Note – plagioclase (light colored feldspar) can also be present up to ~25% ULTRAMAFIC – Peridotite rocks that are composed of minerals that are black and green in color (olivine and pyroxene). Exceptions to color rule – Obsidian is normally dark in color but is FESLIC because it is composed completely of silica. The color is due to ash settling in the cooling lava. Goes hand in hand with the environment where the molten material cooled. INtrusive magma cooled over thousands/millions of years within the earth. The crystals had time to cool, so they are large (visible with your eye). Texture = PHANERITIC Extrusive lava cooled in short period of time at or near the surface. The rocks composed of crystals did not have time to cool, so they are small (not visible with your eye) are APHANITIC VESICULAR texture means that the rock contains holes referred to as vesicles. This occurs when the rock forms faster than the gas can escape the cooling lava. PYROCLASTIC texture is composed of a mixture of volcanic rock fragments, pumice and volcanic ash. Formed from violent eruptions (lots of gas and silica content) GLASSY textures occur in rocks that have rapidly cooled without crystal formation. As with some minerals, they tend to show conchoidal fracture surfaces with luster typical of shards of glass. Combination (extrusive and intrusive) PORPHRYTIC texture results when a few large crystals (phenocrysts) are formed intrusively and brought to the surface by molten material where it cools much faster (matrix or groundmass). SEDIMENTARY ROCKS: Created by 4 processes - weathering, transportation, deposition and diagenesis. Quartz sand, clay and calcite are the main end products of weathering Diagenesis – processes that turn sediments into rocks (compaction, cementation, lithification) Clastic Chemical Biochemical Weathering products of clastic rocks have visible grains (rough/bumpy appearance or texture) or dark colored very fine grains. Classified based on grain size, rounding, and sorting Common Grain Sizes (from coarse to very fine)  Gravel (conglomerate/breccia)  sand (sandstone)  silt (siltstone)  clay (shale) Sorting/rounding depends on amount of time the sediment travels before being deposited  more round/sorted = mature (sediments travelled far before being deposited)  angular/poorly sorted = immature (sediments did not travel far before being deposited) Average grain sizes decreases further from the source River grains > Beach grains > Deep marine grains Quiet/Low Energy environments, (lakes and swamps) will consist mostly of fine-grained particles Wind sorts sediments well Glaciers poorly sort sediments Inorganic chemical rocks form from chemicals that are dissolved in a solution, transported and chemically precipitated out of solution. Common chemical sedimentary rocks include:  carbonate rocks such as oolitic limestone, travertine and dolostone  rocks composed of evaporite minerals such as halite (rock salt) and gypsum rocks that form by replacement of other rocks or minerals such as chert and flint. Composed of skeletons of living plants and animals - overwhelmingly carbonate (remember calcite reacts with acid) Exceptions – chert is composed of radiolarians(organisms with silica skeletons) Common biochemical rocks:  Limestone and dolomite: form from calcareous skeletons of organisms  Coquina: composed of shell fragments (shallow high energy environment).  Chalk: soft, white, porous limestone made of a specific marine microorganism called a coccolithophore (forms in quiet, deep marine waters).  Chert: Like limestone, chert may form from the accumulation of siliceous skeletons Chert also forms by direct (inorganic) precipitation (see below). Coal: Formed from fossilized plant tissue METAMORPHIC ROCKS: Form from parent rock (Protolith) undergoing increases in pressure/temperature/fluid volume Protolith can be igneous, sedimentary or metamorphic Metamorphic Agents – heat, pressure, hydrothermal fluids Metamorphic Textures: Foliated and Non-Foliated Foliated Non-foliated Created in areas undergoing Contact Metamorphism (small scale – localized events, no directional stresses.) Created in areas undergoing Regional Metamorphism (large scale – plate tectonics) Platy minerals align under heat/pressure  Slate – minerals too small to see, splits into thin sheets. LOW GRADE  Phyllite – slaty minerals slightly larger, slight foliation and shine. LOW to MEDIUM GRADE  Schist – Platy minerals visible, shiny sheen. MEDIUM GRADE  Gneiss – distinctive banded appearance. HIGH GRADE Example – hornfels is formed when shale is in contact with a direct heat source, such as a magma chamber, with no addition of pressure OR Regional Metamorphism if the protolith is compositionally uniform. (e.g. quartzite) Parent rock is shale for slate to gneiss (Gneiss can also be made from sandstone or granite that underwent pressure) GEOLOGIC STRUCTURES Faults: Breaks in rock units where movement/displacement has occurred. • Four types: o Normal Fault: hanging wall moves down relative to foot wall. Extensional environment o Reverse/Thrust Fault: hanging wall moves up relative to foot wall. Compressional environment o Strike Slip Fault: No vertical motion, only lateral motion. Can be described using direction of relative motion (Left lateral or Right lateral) o Oblique Slip Fault: Both vertical and horizontal motion. Folds: Bends in rock units where forces have been applied over long periods of time. • Four types o Syncline: U shaped, youngest rocks in center o Anticline: ꓵ shaped, oldest rocks in the center o Basin: 360° syncline, youngest rocks in the center o Dome: 360° anticline, oldest rocks in the center Limb Hinge Example Questions Identification Questions. YOU WILL NOT BE GIVEN CHARTS 1. a. Does this sample have cleavage? If so, what is the name of this type of cleavage? b. What special property of this mineral can be used for identification? 2. a. Is this igneous rock mafic, felsic, intermediate, or ultramafic in composition? b. What is its texture? 3. a. Is this metamorphic rock foliated or non-foliated? b. Is it low, medium, or high metamorphic grade? Multiple Choice Questions – 12 total 1. Extrusive igneous rocks may exhibit which of the following igneous textures: 2. What are examples of Erosional and Metamorphic agents? YOU ARE ULTIMATELY RESPONSIBLE FOR ALL MATERIALS, CONCEPTS, AND PROCEDURES USED IN LAB EXERCISES 1 THROUGH 5. Be able to.... a. recognize physical properties of mineral and rock samples b. identify mineral and rock samples without using classification charts c. utilize provided tools to classify mineral and rock samples d. name the different types of faults and folds, as well as the movement/forces that cause them All Possible Rock and Mineral Samples Minerals Igneous Rocks Sedimentary Rocks Metamorphic Rocks Orthoclase Feldspar Quartz Calcite Plagioclase Feldspar Halite Galena Magnetite Limonite Garnet Biotite Muscovite Olivine Pyroxene Amphibole Talc Graphite Hematite Sulfur Pyrite Fluorite Granite Diorite Basalt Gabbro Rhyolite Andesite Volcanic Tuff Andesite Porphyry Basalt Porphyry Pumice Obsidian Peridotite Scoria Fossiliferous Limestone Micrite Limestone Oolitic Limestone Bituminous Coal Chalk Coquina Chert Arkose Sandstone Sandstone Shale Conglomerate Breccia Rock Salt Rock Gypsum Slate Schist Phyllite Gneiss Hornfels Quartzite Marble Serpentinite Anthracite Coal

Example midterm questions:

• Halite

  • Does this sample have cleavage? If so, what is the name of this type of cleavage 

  • What special property of this mineral can be used for identification 

• Gabbro

  • Is this igneous rock mafic, felsic, intermediate, or ultramafic 

    • Mafic 

  • What type of texture does it have

    • Phaneritic 

Sedimentary rock: rocks formed from sediment 

• Grains + cement = rocks 

What is sediment?

• Dictionary definition: 

  • The matter that settles to the bottom of a liquid 

• Use this definition: 

  • Material derived from pre-existing rock, from biogenic sources, or precipitated by chemical processes, and deposited at, or near, the earth's surface 

How do we make sedimentary rocks?

• Four big processes 

1. Weathering 

2. erosion/transportation 

Weathering: processes acting on Earth’s surface to break down pre-existing rock 

• Two types

  • Chemical: breakdown by chemical agents, minerals in a rock may change, processes like oxidation or dissolution 

  • Mechanical: physically breaking down rocks into smaller pieces (no change in chemistry, creates clasts: smaller fragments of rocks)

• Left with 3 products after weathering  

  • Quartz sand 

  • Clay 

  • Minerals in solution 

Erosion: transportation away from the place of weathering  

• Water: most important means of erosion 

  • Rivers, rainwater, oceans, tides

• Ice

  • Glaciers 

• Wind

  • Sand dunes

• Gravity 

  • Landslides 

Deposition: the importance of energy 

Diagenesis: putting the pieces together 

• Lithification: process where sediments compact under pressure, expel fluids, and become solid rock 

  • Compaction: pressure from overlying sediments causes reduction of pore space and removal of water

  • Cementation: precipitation of secondary minerals from solution fills pore spaces and binds grains together

  • After lithification, grains of sediment, rock fragments and fossils can be replaced by other minerals 

Types of sedimentary rocks 

Clastic: made from broken pieces of rock cemented together 

Chemical: made from minerals being dissolved into water and precipitated oit 

• Inorganic (chemical)

• Organic (biochemical)

Grain size: increase in grain sized leads to an increase in energy needed for transportation 

• Major terms: gravel, sand, silt, clay 

Coarse grains 

• Gravel and sand 

  • Particles large enough to see 

  • If some scratch glass, the rock is clastic

Fine grains 

• Silt and clay 

  • Particles too small to see

  • If the rock is dark in color, dense, and shows prominent layering the rock is clastic 

  • All other fine grained rocks are chemical or biochemical 

Well sorted sediment = little variation in grain size 

Poorly sorted sediment = wide range of grain sizes

Rounding: how smooth a grain is 

• Well rounded =  smooth surfaces 

• Sorting and rounding correspond to distance or time a grain is transported 

Breccia: more angular, not as well rounded

Conglomerate: well rounded, transported a greater distance 

Maturity: how far removed a rock is from its source, igneous minerals have a lot of amphibole

Mature quartz sandstone 

Immature arkosic sandstone 

Chemical sedimentary rocks 

• Evaporites 

• Carbonates

• chert/flint 

Evaporites

Halite 

• NaCl 

Gypsum 

Carbonates: form form chemical leaching and precipitation 

• Removing elements from minerals, deposited elsewhere 

• Can be chemical or biochemical

• Other inorganic processes can affect formation 

Biochemical sedimentary rocks: may be predominantly clastic or biogenic 

• Limestone, coquina, chalk, chert 

• Organic: formed due to decomposition of organic remains under higher temperatures 

Limestones: made of finely crushed remains of shelled marine organisms 

• Micrite 

• Fossiliferous 

Coquina: poorly cemented shell fragments 

• Shells and cement are both composed of calcite 

• Forms in warm, high energy shallow marine environments 

Chalk: soft white, porous limestone

• Made from marine microorganisms classed coccolithophores 

• Forms in quiet, deep marine waters 

Coal: fossilized plant tissue, formed in a bog 

bio

Chert: secretly quartz, can be chemical or biochemical, may form from the accumulation of silica skeletons from microscopic organism or by replacement of other rocks, minerals, and organic matter after deposition 

3/10/25 Midterm Review 

Cooling history 

• phaneritic texture: cools very slowly, time for big crystals to develop, cooling history intrusive 

  • Big crystals mean at some point it was cooling slowly 

• Obsidian: texture – glassy 

• Vesicles: cooling outside, cooling quickly, extrusive 

• No crystals: cooling quickly, cooling extrusively, no time to grow any crystals 

Clast: piece of a rock 

Biochemical and chemical rocks: processes that result in the creation of the rock in addition to the elements necessary for the formation and where they come from 

• Pink in color, reddish, halite: rock salt, forms through removing all the water from a given area, same class as rock gypsum – chemical rock 

• Bituminous coal: starts out as trees, fall over in a swamp and get buried, originally it is made from something organic – biochemical rock 

• Cochina: made from pieces of broken up shells that get cemented together – Biochemical rock (the material it is made from was originally part of an organism) 

• Chert: forming from silica or tiny little microorganisms – either chemical or biochemical