Geology 101L Exam 1 Study Guide PDF

Geology 101L – Exam 1 Study Guide  You will have your rock and mineral identification sheets for reference!!  You will be using them to identify rocks and minerals  Rock identification: fill in the blank questions leading up to mineral identification (like in lab)  Matching, fill...

Geology 101L – Exam 1 Study Guide  You will have your rock and mineral identification sheets for reference!!  You will be using them to identify rocks and minerals  Rock identification: fill in the blank questions leading up to mineral identification (like in lab)  Matching, fill in the blank, true/false, multiple choice GENERAL Define igneous, sedimentary, and metamorphic rocks. Igneous Rocks: Formed from the solidification of molten rock (magma or lava). Types include: Intrusive: Cools slowly underground (e.g., granite).Extrusive: Cools quickly on the surface (e.g., basalt). Sedimentary Rocks: Created from the accumulation and compaction of sediments or the precipitation of minerals. Types include: Clastic: Made from rock fragments (e.g., sandstone). Chemical: Formed from mineral precipitation (e.g., limestone). Organic: Composed of biological material (e.g., coal). Metamorphic Rocks: Result from the alteration of existing rocks under heat and pressure. Types include: Foliated: Has layered appearance (e.g., schist). What is a special property of calcite and all rocks containing it? Non-foliated: Lacks layers (e.g., marble). A special property of calcite (CaCO₃) and all rocks containing it is that they react with hydrochloric acid (HCl) by effervescing, or fizzing. This reaction produces carbon dioxide gas, which is a key characteristic used to identify calcite in rocks like limestone and marble. Additionally, calcite has a distinct cleavage and can exhibit double refraction, where light MINERALS (~5 samples) passing through it splits into two rays. Know how to identify the following mineral properties in hand sample  Cleavage Look for smooth, flat surfaces where the mineral breaks. Cleavage planes can be observed by gently applying pressure or by tapping the mineral. Note how it splits along these planes.  Fracture If the mineral doesn’t show cleavage, examine the way it breaks. Fracture can be uneven, conchoidal (curved like a shell), or splintery. This is best seen when breaking a small piece of the mineral.  angle between cleavage planes If the mineral has cleavage, use a protractor or compare it to known angles. Common angles are 90° (like in fluorite) or 120° (like in biotite).  hardness Use the Mohs scale of hardness to scratch the mineral with common objects (e.g., fingernail = 2.5, copper penny = 3.5, glass = 5.5, steel file = 6.5). Determine where the mineral falls on the scale.  luster (metallic or non metallic) Observe how the mineral reflects light. Metallic luster looks shiny and resembles metal, while non-metallic can be glassy, pearly, dull, or earthy.  streak Rub the mineral across a white porcelain streak plate. The color of the powder left behind is the streak color, which can help identify the mineral, regardless of its external color.  striations Look closely at the surface of the mineral for fine, parallel lines. These are commonly found in some plagioclase feldspars and can help differentiate similar minerals.  effervescence (reaction to acid) Place a drop of dilute hydrochloric acid on the mineral. If it fizzes or bubbles, the mineral likely contains carbonate minerals, such as calcite or dolomite.  transparent or opaque Hold the mineral up to a light source. If you can see through it, it’s transparent. If not, it’s opaque. Some minerals can be translucent, allowing some light to pass through but not clear outlines. Is color always a good property to use when identifying minerals? Color can be a helpful property for identifying minerals, but it's not always reliable. Many minerals can come in various colors due to impurities or variations in composition, which can lead to confusion. For example, quartz can be found in colors like clear, purple (amethyst), or smoky. What are the 5 things a material must be/have to be considered a mineral? To be considered a mineral, a material typically must meet the following five criteria: Naturally Occurring: Minerals must form through natural geological processes, not synthetic ones. Inorganic: Minerals are generally inorganic, meaning they are not made from living organisms. Solid: They must be solid at standard temperature and pressure. Definite Chemical Composition: Minerals have a specific chemical formula that defines their composition, though some variations (like solid solutions) can occur. Ordered Internal Structure: Minerals have a crystalline structure, meaning their atoms are arranged in a systematic, repeating pattern. These properties help distinguish true minerals from other substances like rocks or organic materials. IGNEOUS ROCKS (~4 samples)  Know how to identify the following textures in hand sample AND whether they are intrusive or extrusive:  aphanitic Fine-grained texture, too small to see individual crystals without magnification. Usually feels smooth. Extrusive.  phaneritic Identification: Coarse-grained texture, with crystals that are large enough to be seen with the naked eye. Intrusive or Extrusive: Intrusive.  vesicular Identification: Contains small holes (vesicles) formed by gas bubbles. Typically light and porous. Intrusive or Extrusive: Extrusive.  glassy Identification: Smooth, glassy appearance with no visible crystals. It often breaks with a conchoidal fracture. Intrusive or Extrusive: Extrusive. Know how to identify the following colors in hand sample  mafic Dark-colored minerals (like olivine, pyroxene, and amphibole) that are rich in magnesium and iron. Typically look black or dark green.  intermediate A mix of light and dark minerals, often gray or beige. Contains minerals like amphibole and plagioclase.  felsic Light-colored minerals (like quartz and feldspar) that are rich in silica. Typically look white, pink, or light gray. What is the difference between magma and lava? Magma: Molten rock located beneath the Earth's surface. Lava: Magma that has reached the Earth's surface through a volcanic eruption. What does crystal size indicate about rock formation time? Crystal Size: Larger crystals indicate slower cooling, typically associated with intrusive rocks, which cool beneath the surface. Smaller crystals indicate faster cooling, characteristic of extrusive rocks, which cool quickly after being expelled onto the surface. Where do extrusive rocks form? Intrusive? Extrusive Rocks: Form on the Earth's surface from volcanic eruptions (e.g., lava flows, ash deposits). Intrusive Rocks: Form beneath the Earth's surface from magma cooling slowly (e.g., granite, diorite). What two plate boundaries do volcanoes happen at? Convergent Boundaries: Where an oceanic plate subducts beneath a continental or another oceanic plate, leading to volcanic activity (e.g., the Cascades). Divergent Boundaries: Where tectonic plates are moving apart, allowing magma to rise and create new crust (e.g., mid-ocean ridges). SEDIMENTARY ROCKS (~5 samples) Know how to identify these properties in hand sample:  well and poor sorting Well Sorting: The grains are similar in size and shape, indicating they have been sorted by a natural process (like water or wind). The texture appears uniform. Poor Sorting: The grains vary widely in size and shape. You can see large and small grains together in the same sample, creating a mixed appearance.  clast/grain size Very fine: smaller than 0.0625 mm (like clay). Fine: 0.0625 mm to 0.25 mm (like silt). Medium: 0.25 mm to 2 mm (like sand).  angular and rounded grains Coarse: 2 mm to 64 mm (like granules). Angular: Grains have sharp edges and corners, indicating limited transport. Very coarse: larger than 64 mm (like pebbles or Rounded: Grains have smooth, curved edges, indicating they have traveled further and experienced abrasion. cobbles). Know what biogenic, chemical, and clastic rocks are Biogenic Rocks-Formed from organic material. Chemical Rocks-Formed from the precipitation of minerals from solution. Clastic Rocks-Composed of fragments of pre-existing rocks that are cemented together. How does the distance traveled from its source influence rounding of a grain? ‘ The distance traveled from its source influences the rounding of a grain because as grains are transported, they collide with each other and other surfaces. This abrasion causes the edges to wear down and become smoother. The longer the distance a grain travels, the more rounded it typically becomes due to continuous friction and impact, resulting in a more polished appearance. What is the difference between weathering and erosion? Weathering is the process of breaking down rocks and minerals at their original location through physical, chemical, or biological means. It does not involve movement. Erosion, on the other hand, is the removal and transportation of weathered material from one location to another by natural forces such as water, wind, or ice. Essentially, weathering breaks down materials, while erosion moves them.