How the Earth works Lecture 5: Mineralogy and Sedimentology

Question 1

What are the four classes of sedimentary rock?

Answer 1

Clastic—loose rock fragments (clasts) cemented together.

Biochemical—cemented shells of organisms.

Organic—carbon-rich remains of once living organisms.

Chemical—minerals that crystallize directly from water.

Question 2

Define and list form of chemical weathering

Answer 2

Dissolution (e.g. minerals dissolve in rainwater)

Hydrolysis (e.g. acid water breaks down feldspar to form clay)

Oxidation (Fe-bearing minerals combine with oxygen to form easily-weathered oxides)

Hydration (incorporation of water into the crystal lattice causes swelling and expansion)

Question 3

Define Lithification

Answer 3

Transforms loose sediment into solid rock.

Question 4

List the variables on which sedimentary rocks are classified

Answer 4

Clast (grain) size
Sorting
Angularity and sphericity
Composition of clasts
Composition of cement

Question 5

Define clast size

Answer 5

Clast size—the diameter of fragments or grains

Range from very coarse to very fine
Boulder, cobble, pebble, sand, silt, and clay

Gravel—coarse-grained sed (boulder, cobble, pebble)
Mud—fine-grained (silt and clay)

Question 6

Define clast size

Answer 6

Clast size—the diameter of fragments or grains
Range from very coarse to very fine
Boulder, cobble, pebble, sand, silt, and clay
Gravel—coarse-grained sed (boulder, cobble, pebble)
Mud—fine-grained (silt and clay)

Question 7

Describe the role of angularity and sphericality in sediment

Answer 7

Sphericity
Fresh detritus = angular and nonspherical
Grain roundness and sphericity increases with transport
Well-rounded—long transport distances
Angular—negligible transport

Question 8

Define maturity

Answer 8

Maturity—the degree of sediment processing

Sediments become gradually made up of exclusively one. E.g. eventually is only made up small quartz crystals

Question 9

Define clast composition

Answer 9

Clast composition—the mineral makeup of sediments

May be individual minerals or rock fragments

Composition yields clues about the original source rock

Question 10

Define the nature of cement

Answer 10

Nature of cement—minerals that fill sediment pores

Fluids with dissolved solids flush through pore system
Dissolved ions slowly crystallize and fill pores

Question 11

Define a conglomerate

Answer 11

Rounded rock clast

Question 12

Define sandstone

Answer 12

Clastic rock made of sand sized particles

Question 13

Define fine clastics

Answer 13

Clastic rocks deposited in calm water environments

Question 14

Define limestone

Answer 14

Sedimentary rocks made up of Calcium Carbonate (CaCO3)

Biochemical limestone is CaCO3 skeletal remains