Sedimentary Rocks Review

Quiz Instructions

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Igneous Rock Identification

Types of Igneous Rocks

Gabbro

  • Classification: Intrusive

  • Texture: Phaneritic

  • Composition: Mafic

Diorite

  • Classification: Intrusive

  • Texture: Phaneritic

  • Composition: Intermediate

Granite

  • Types:

    • Pink Granite

    • White Granite

  • Classification: Intrusive

  • Texture: Phaneritic

  • Composition: Felsic

Porphyritic Rocks

  • Definition: Rocks with dual cooling history leading to a porphyritic texture.

  • Examples:

    • Porphyritic Rhyolite (Felsic)

    • Porphyritic Andesite (Intermediate)

    • Porphyritic Basalt (Mafic)

Basalt

  • Classification: Extrusive

  • Texture: Aphanitic

  • Composition: Mafic

Rhyolite

  • Classification: Extrusive

  • Texture: Aphanitic

  • Composition: Felsic

  • Website: www.MiniMeGeology.com

Obsidian

  • Classification: Extrusive

  • Texture: Glassy

  • Note: Cannot determine composition from color.

Scoria

  • Classification: Extrusive

  • Texture: Vesicular

  • Composition: Intermediate/Mafic

Pumice

  • Classification: Extrusive

  • Texture: Vesicular

  • Composition: Felsic

Peridotite

  • Classification: Intrusive

  • Texture: Phaneritic

  • Composition: Ultramafic

  • Note: Olivine is the mineral; Peridotite is the rock.

Exam Preparation

  • Instruction: Be able to use provided chart for lab procedures, memorization not required.

Lab 3: Sedimentary Rocks

Classification of Sedimentary Rocks

  • Broad Categories:

    • Clastic

    • Non-clastic

Clastic Sedimentary Rocks

  • Definition: Composed of clasts (grains of eroded rocks).

  • Classification based on size of clasts (coarse to fine).

Sorting and Roundness of Clastic Sedimentary Rocks

  • Sorting Categories:

    • Very Poorly Sorted

    • Poorly Sorted

    • Moderately Sorted

    • Well Sorted

    • Very Well Sorted

Descriptions of Sort

  • Roundness:

    • Angular (sharp edges)

    • Subangular

    • Subrounded

    • Well-rounded (smooth edges)

  • Increasing abrasion during transportation affects roundness.

  • Poorly sorted: various grain sizes.

  • Well sorted: grains nearly equivalent in size.

Grain Size Classification

  • Clay: Very fine grained (<1/256 mm), NOT visible to naked eye.

  • Silt: Fine grained (1/16-1/256 mm), NOT visible to naked eye.

  • Sand: Medium grained (1/16-2 mm), Visible to naked eye.

  • Gravel: Coarse grained (>2 mm), Visible to naked eye.

Depositional History of Clastic Sedimentary Rocks

  • Roundness and sorting give clues about depositional history.

  • Well sorted and well-rounded grains are indicators of longer transport distances.

  • Longer exposure to weathering due to more collisions.

Depositional Environments

  • Definition: Locations where clasts settle out of solution.

  • Energy Level: High or low energy.

  • Types of Environments:

    • Continental (e.g., deserts, riverbeds)

    • Transitional (e.g., deltas, beaches)

    • Marine (e.g., ocean floors, shelf/platforms)

High Energy Environments

  • Example: Fast-moving water (rivers, shallow seas).

  • Capable of carrying larger grains; sedimentary rocks formed here typically have larger clasts.

Low Energy Environments

  • Example: Slow-moving water (bottom of lakes, deep marine).

  • Smaller grains are allowed to settle out due to the low energy.

Very Low Energy Environments

  • Example: Still water.

  • Even the smallest clasts can settle out of solution.

Non-Clastic Sedimentary Rocks

  • Two main categories:

    • Chemical

    • Biochemical

Chemical Sedimentary Rocks

  • Formation: Occur from the precipitation of minerals in water.

  • Common types include:

    • Limestone

    • Evaporites

    • Chert

  • Characteristic: Made of carbonates; react by fizzing in response to hydrochloric acid (HCl).

Biochemical Sedimentary Rocks

  • Definition: Formed through microorganisms extracting chemical components from water and incorporating them into hard parts.

  • Example: Foraminifera incorporating minerals into their shells.

Non-Clastic Rock Textures

  • Crystalline: Sedimentary rock composed of crystals accumulated from crystalline material.

    • Example: Rock Salt, Alabaster.

  • Amorphous (cryptocrystalline): Dense rock with fine, non-crystalline material, often deposited by chemical precipitation.

    • Example: Chert.

  • Fossiliferous: Term used for limestones containing abundant fossils.

    • Example: Fossiliferous limestone.

Peat and Lignite

  • Definition: Derived from plant material accumulating in marshes/swamps.

  • Not classified as minerals, but share formation processes similar to diagenesis (rock formation).

Rocks vs. Minerals

  • Important Distinction: Rocks are made up of one or more minerals.

  • Types of Rocks:

    • Single mineral rocks: Rock salt, alabaster.

    • Multi-mineral rocks: Granite, dolomite, basalt, etc.

Overview of Rock Cycle

  • Igneous rocks: Form when magma or lava cools.

  • Processes: Igneous rocks can be subject to erosion, metamorphosis, or melting.

  • Sedimentary rocks: Form when eroded rock material is deposited, compacted, and cemented.

  • Similar processes apply to sedimentary rocks (erosion, metamorphosis, melting).

Lab 3 Instructions

  1. Determine if the rock is clastic or non-clastic (most non-clastic rocks are soft).

  2. If clastic:

    • a. Determine grain size using a ruler.

    • b. Utilize "grain size" column (Table 3.1) to classify as gravel, sand, silt, or clay.

    • c. Use the "characteristics" column to determine rock name.

    • d. Note the size, sorting, and roundness of clasts via the "characteristics" column.

    • e. Reference Table 3.2 to determine the depositional environment (continental, transitional, marine).

    • Note: Specific depositional environments won't need to be recorded for lab/exam. For the "composition/mineralogy %" column, CROSS OUT the %. This is not required for lab.

  3. If non-clastic:

    • a. Determine composition, starting with non-calcium carbonate rocks.

    • b. Conduct an HCl test if you suspect a calcium carbonate rock.

    • c. Consult the "characteristics" column (Table 3.3) for rock naming.

    • d. Document other characteristics of the rock.

    • e. Use Table 3.4 to identify the depositional environment (is it continental, transitional, marine?).

    • Note: Just like with clastic rocks, no need for specifics on depositional environments for lab/exams.