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sandstones Flashcards

1
Q

what size of particles constitute framework fraction of sandstones?

A

sand and coarse silts

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2
Q

framework grains of sandstones are composed predominantly (90-95%) of:

A

quartz, feldspar, and rock fragments

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3
Q

what minerals constitute matrix of sandstones?

A

clay minerals

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4
Q

heavy minerals (accessory minerals) associated with sandstones:

A

zircon, rutile, tourmaline

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5
Q

high temp varieties of quartz

A

cristobalite and tridymite

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6
Q

fibrous quartz:
amorphous silica:

A

chalcedony ; opal

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7
Q

principal crystalline varieties of SiO2

A

quartz, cristobalite, tridymite

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8
Q

t or f: opal is hydrous

A

t

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9
Q

range of abundance of quartz in composition of sandstone:

A

<5% to >95%

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10
Q

when a sandstone has abundant quartz, it means that:

A

it is stable and has high resistance to weathering

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11
Q

range of feldspar as sandstone constituent

A

0-60%

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12
Q

sandstones containing _____ of feldspars are considered “feldspar-rich”

A

> 25%

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13
Q

rock fragments may be hard to identify due to

A

nature of

deposition, transport, weathering, diagenesis

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14
Q

rock fragments can go up to _____ on lithic sandstones

A

> 50%

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15
Q

wackes compose how many percent matrix/mud?

A

> 5-10%

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16
Q

cements occur as:

A

silica (microquartz), carbonates, hematite

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17
Q

which type of feldspar is generally more abundant in an average sandstone? and why?

A

potassium feldspar;

because it is more stable than plag feldspar and is more compatible to be with quartz (refer to bowen’s)

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18
Q

sandstone composed of calcite grains

A

calcareous sandstone

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19
Q

this sandstone would most likely be developed along composite volcanoes

A

arkose

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20
Q

what are the members of the alkali feldspars?

A

solid solution series from:

K(AlSi3O8) orthoclase, sanidine, microcline to Na(AlSi3O8) anorthoclase

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21
Q

members of plagioclase feldspars?

A

from Calcium rich to sodium rich:

anorthite, bytownite, labradorite, andesine, oligoclase, albite

22
Q

this is the measure of the mineralogic maturity of heavy-mineral assemblages in sandstones

A

ZTR index (zircon-tourmaline-rutile)

23
Q

what does it mean when a sandstone has a high amount of stable minerals?

A

the sandstone has undergone intensive weathering or sediment recycling

24
Q

two broad classification of sandstones:

A

epiclastic and volcaniclastic

25
Q

what does it mean when a sandstone has a high amount of stable minerals?

A

the sandstone has undergone intensive weathering or sediment recycling

26
Q

these deposits are formed from fragments of pre-existing rocks derived by weathering and erosion

A

epiclastic deposits

27
Q

matrix is defined as materials __________ in size

A

less than 0.03 mm (30 microns)

28
Q

draw the composition of sandstones ppt ni sir (mix of pettijohn and gilbert’s)

A
29
Q

percent of matrix in arenites

A

<5%

30
Q

three origins of quartz arenite:

A

stream, wind, and coastal transport

31
Q

textural inversions in quartz arenite are most likely because of?

A

mixing of grains from different sources and environmental variables

32
Q

quartz arenites are most common on what environment?

A

eolian

33
Q

under what weathering conditions are quartz arenites formed? why?

A

quartz arenites are formed under intensive and vigorous weathering, thereby eliminating unstable components

34
Q

t or f: carbonates and hematites are stable as cementing materials rather than stand alones

A

t

35
Q

typical texture of quartz arenites:

A

mature to supermature

36
Q

a sandstone is considered feldspathic if it has _______ feldspar;

a sandstone is considered arkose if it has _____ feldspar

A

> 10% ; >25%

37
Q

explain why felspar-rich sandstones are formed close to sources

A

because feldspars are prone to weathering, thus they only survive in very little amount of weathering and transpo

38
Q

what are the cements of feldspathic arenite?

A

carbonates, hematite, sulfates, clay minerals, authigenic quartz and feldspars

39
Q

t or f: feldspathic arenite is typically coarse grained

A

t

40
Q

what causes the pink or red color in feldspathic arenite?

A

due to k-feldspars or iron oxides

41
Q

shape of grains of feldspathic arenites

A

sub-angular to angular (immature to submature)

42
Q

explain the correlation of the grain size and abundance of feldspar in feldspathic arenites

A

there is an inverse relationship between the two, owing to the tendency of feldspars to break into smaller fragments during transport

43
Q

feldspathic arenites originates in:

A
  1. very cold or very arid climatic conditions where chemical weathering is eliminated
  2. in warmer, more humid climate with high relief and rapid erosion before decomposition
44
Q

residual arkose vs transported arkose

A
45
Q

t or f: lithic arenites have salt and pepper appearance

A

t

46
Q

t or f: lithic arenites have low textural variations

A

f (large textural variations)

47
Q

matrix of lithic arenites can go up to _____

A

> 30%

48
Q

volcaniclastics classification diagram

A
49
Q

this type of sandstone contains some amounts of glauconite

A

greensands

50
Q

what are the cements of feldspathic arenite?

A

carbonates, hematite, sulfates, clay minerals, authigenic quartz and feldspars

51
Q

composition of volcaniclastic sandstones:

A

glassy fragments, crystals, lithics

52
Q

volcaniclastics alters to

A

smectite, zeolite, silica, glass

sp (7 decks)

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