Page 176 - Laboratory Manual in Physical Geology

ACTIVITY Sedimentary Processes
Sedimentary processes ( FIGURE 6.1 ) include every-
6.4 Biochemical and Chemical thing from the time and place that sediment forms to
Sediment and Rock the time and place where it is lithified (hardened into
sedimentary rock).
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THINK What are sedimentary rocks made of, Formation of Chemical Sediment
About It and how are they formed?
Water is a solvent (a liquid capable of dissolving and
dispersing solid materials), so all natural bodies of water
OBJECTIVE Analyze characteristics of biochemical and are aqueous solutions. This means that they are filled with
chemical sediment and rock and infer how they form.
chemicals that are “in solution,” dissolved and dispersed
PROCEDURES from the materials over and through which the water
1. Before you begin, read about Sedimentary has flowed. When water full of dissolved chemicals (an
Processes and Composition and Textures of aqueous solution) evaporates, the chemicals in the water
Sediments and Sedimentary Rocks below. Also, combine and precipitate (form solids from the solution)
this is what you will need: as mineral crystals and chemical residues called chemical
sediment . Chemical sediment is generally in situ, meaning
___ Activity 6.4 Worksheet (p. 176 ) and pencil that it formed where it is found. For example, think of the
___ dilute HCl (hydrochloric acid) in dropper intergrown halite crystals in rock salt that formed in an
bottle
___ seashells, charcoal briquette evaporating sea. The crystals are intergrown and locked
together as sedimentary rock as they form. Oxide residues,
___ coal, dolomite like rust, are often deposited in situ (in place, where the
___ hand lens rust formed) as coatings on surfaces of rocks, but they can
___ plastic sandwich bags also form as powdery residues in the water and be carried
___ piece of chalk from the chalkboard
by the water to new locations.
2. Then follow your instructor’s directions for Chemical sediment is the end product of chemical
completing the worksheets. weathering —the decomposition or dissolution of
Earth materials. For example, feldspars are a group
of the most common minerals in Earth’s crust. When
potassium feldspar decomposes in acidic groundwater,
ACTIVITY it chemically decays to clay minerals (kaolinite) plus
chemicals (potassium and silica) in solution. This is
6.5 Sediment Analysis, the main way that clay forms to make soil. Olivine
decomposes to iron and magnesium in solution, and
Classification, and then they combine with oxygen to make oxide residues,
Interpretation like rust. Chemical residues commonly coat the
surfaces of visible grains of sediment and either discolor
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THINK What are sedimentary rocks made of, them or serve as a cement to “glue” them together and
About It and how are they formed? form sedimentary rock.
Formation of Clastic (Detrital) and
OBJECTIVE Describe and classify samples of
sediment in terms of texture and composition, and Biochemical Sediment
then infer environments in which they formed. Physical (mechanical) weathering is the cracking, crushing,
and wearing away (scratching, abrasion, transportation) of
PROCEDURES
Earth materials. Cracking and crushing processes cause big
1. Before you begin, read about Sedimentary rocks to be fragmented into clasts (broken pieces: from the
Processes, Composition, and Textures of Greek klastós , meaning broken in pieces) or clastic sediment ,
Sediments and Sedimentary Rocks below. Also, including rock fragments and mineral grains (whole crystals
this is what you will need: or fragments of crystals). Continental bedrock, rich in
___ Activity 6.5 Worksheet (p. 178 ) and pencil silicate minerals, is fragmented into siliciclastic sediment
___ Visual Estimation of Percent chart from made of quartz grains, feldspar grains, and rock fragments.
GeoTools 1 or 2 Sediment worn and transported from the land, generally
2. Then follow your instructor’s directions for siliciclastic, is also called detrital sediment (from the
completing the worksheets. Latin detritus , participle of detero , meaning to weaken,
wear away, rub off ). Rock fragments and mineral crystals

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