Chapter 5 Flashcards
What are framework grains?
The sediment size of silicate minerals and rock fragments
How much does quartz make up of the framework?
50 to 60%
How do you distinguish feldspars from quartz under the microscope?
Quartz has undulatory extinction.
How do you distinguish between alkali and plagioclase feldspars?
Chemical composition
How much do feldspars make up of the framework?
10 to 20%
How much do sandstones make up of all sedimentary rocks?
20 to 25%
What is the size range for grains in sandstones?
(1/16th-2mm)
How much do rock fragments make up of the framework?
15-20%
What are the kinds of cement?
Can be of silicate or carbonate origin
What is syntaxial overgrowth?
Quartz cement that retains the crystallography of the actual grain
How are carbonate cements formed?
precipitated through pore space in framework grains
What is a matrix mineral?
Grains in sandstones that are less than 0.03mm that fill space
What are the clay mineral groups?
Illite, smectite, kaolinite, chloride
What are sandstones that are free of matrix (less than 5%) known as?
Quartzarenites, feldspathic arenites, litic arenites
When is the term arkose used?
Arkose is used in feldspathic arenites that is less greater than 25% feldspars
When is the term greywacke used?
a matrix rich sandstone that is dark green/gray and very hard
What is compositional maturity?
The relative abundance of stable and unstable grains in a sandstone
What is a mature sandstone?
A sandstone of mostly quartz
What is an immature sandstone?
Sandstone of mostly unstable (feldspars)
What is textural maturity?
The relative abundance of matrix and the degree of roundness and sorting of framework grains
What is texturally mature?
No clay, well sorted grains that are well rounded
What is texturally immature?
Much clay, poorly sorted and angular framework grains
What does textural maturity represent?
the degree of sediment transport and reworking
What are quartz arenites composed of?
greater than 90% silica grains
What are the common colors?
Light gray, can be stained red, pink, yellow, or brown
what is the textural maturity of quartz arenites
Mature to super mature
What is the percentage of quartz arenites in all sandstones?
!/3rd of all sandstones
What is the composition of feldspathic arenites?
less than 90% quartz
What are the common colors of feldspathic arenites?
Pink/red
light gray to white
What is the grain size/ shape of feldspathic arenites?
medium to coarse
angular to subangular
What is the amount of matrix in f-arenites?
trace amounts to 15%
What is the textural maturity of f-arenites?
Immature to sub-mature (wacke)
What is the composition of lithic arenites?
More unstable rock fragments than feldspars
What is the composition of l-arenites?
immature sandstones
What is the grain size in conglomerates?
at least 30% grains bigger than 2mm
What is a monomict conglomerate?
stable conglomerates composed of a single clast type
What is a polymict conglomerate?
a conglomerate that contains an assortment of many clasts types
What is a petromict conglomerate?
Polymicts that are composed of unstable or metastable clasts
What is monomict derived from?
Sedimentary rocks containing quartzite beds
What is petromict derived from?
volcanic, metamorphic, or sedimentary rocks
one type is dominant clast
What is intraformational derived from?
clast sediments formed within a depositional basin
flat pebble conglomerates
What is the grain size in shales?
Fine sized grains between 1/16th-1/256mm that make up more than 50% of the rock?
What is a shale?
A rock with silt size grains that has laminations?
What is a mudrock?
a rock with silt size grains without laminations
What is the composition of shales/mudrocks?
Clay minerals, free of quartz and feldspars
what is a mudstone?
33-65% clay size constituents
What is a mud shale?
33-65% with laminations
What is a claystone?
66-100% clay grains
What is a clay shale?
66-100% with laminations
What is the diagenetic process of clastic rocks?
Uplict to burial and sedimentation
