sandstones

Question 1

what size of particles constitute framework fraction of sandstones?

Answer 1

sand and coarse silts

Question 2

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

Answer 2

quartz, feldspar, and rock fragments

Question 3

what minerals constitute matrix of sandstones?

Answer 3

clay minerals

Question 4

heavy minerals (accessory minerals) associated with sandstones:

Answer 4

zircon, rutile, tourmaline

Question 5

high temp varieties of quartz

Answer 5

cristobalite and tridymite

Question 6

fibrous quartz:
amorphous silica:

Answer 6

chalcedony ; opal

Question 7

principal crystalline varieties of SiO2

Answer 7

quartz, cristobalite, tridymite

Question 8

t or f: opal is hydrous

Answer 8

t

Question 9

range of abundance of quartz in composition of sandstone:

Answer 9

<5% to >95%

Question 10

when a sandstone has abundant quartz, it means that:

Answer 10

it is stable and has high resistance to weathering

Question 11

range of feldspar as sandstone constituent

Answer 11

0-60%

Question 12

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

Answer 12

> 25%

Question 13

rock fragments may be hard to identify due to

Answer 13

nature of

deposition, transport, weathering, diagenesis

Question 14

rock fragments can go up to _____ on lithic sandstones

Answer 14

> 50%

Question 15

wackes compose how many percent matrix/mud?

Answer 15

> 5-10%

Question 16

cements occur as:

Answer 16

silica (microquartz), carbonates, hematite

Question 17

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

Answer 17

potassium feldspar;

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

Question 18

sandstone composed of calcite grains

Answer 18

calcareous sandstone

Question 19

this sandstone would most likely be developed along composite volcanoes

Answer 19

arkose

Question 20

what are the members of the alkali feldspars?

Answer 20

solid solution series from:

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

Question 21

members of plagioclase feldspars?

Answer 21

from Calcium rich to sodium rich:

anorthite, bytownite, labradorite, andesine, oligoclase, albite

Question 22

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

Answer 22

ZTR index (zircon-tourmaline-rutile)

Question 23

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

Answer 23

the sandstone has undergone intensive weathering or sediment recycling

Question 24

two broad classification of sandstones:

Answer 24

epiclastic and volcaniclastic

Question 25

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

Answer 25

the sandstone has undergone intensive weathering or sediment recycling

Question 26

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

Answer 26

epiclastic deposits

Question 27

matrix is defined as materials __________ in size

Answer 27

less than 0.03 mm (30 microns)

Question 28

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

Question 29

percent of matrix in arenites

Answer 29

<5%

Question 30

three origins of quartz arenite:

Answer 30

stream, wind, and coastal transport

Question 31

textural inversions in quartz arenite are most likely because of?

Answer 31

mixing of grains from different sources and environmental variables

Question 32

quartz arenites are most common on what environment?

Answer 32

eolian

Question 33

under what weathering conditions are quartz arenites formed? why?

Answer 33

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

Question 34

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

Answer 34

t

Question 35

typical texture of quartz arenites:

Answer 35

mature to supermature

Question 36

a sandstone is considered feldspathic if it has _______ feldspar; a sandstone is considered arkose if it has _____ feldspar

Answer 36

>10% ; >25%

Question 37

explain why felspar-rich sandstones are formed close to sources

Answer 37

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

Question 38

what are the cements of feldspathic arenite?

Answer 38

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

Question 39

t or f: feldspathic arenite is typically coarse grained

Answer 39

t

Question 40

what causes the pink or red color in feldspathic arenite?

Answer 40

due to k-feldspars or iron oxides

Question 41

shape of grains of feldspathic arenites

Answer 41

sub-angular to angular (immature to submature)

Question 42

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

Answer 42

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

Question 43

feldspathic arenites originates in:

Answer 43

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

Question 44

residual arkose vs transported arkose

Question 45

t or f: lithic arenites have salt and pepper appearance

Answer 45

t

Question 46

t or f: lithic arenites have low textural variations

Answer 46

f (large textural variations)

Question 47

matrix of lithic arenites can go up to _____

Answer 47

>30%

Question 48

volcaniclastics classification diagram

Question 49

this type of sandstone contains some amounts of glauconite

Answer 49

greensands

Question 50

what are the cements of feldspathic arenite?

Answer 50

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

Question 51

composition of volcaniclastic sandstones:

Answer 51

glassy fragments, crystals, lithics

Question 52

volcaniclastics alters to

Answer 52

smectite, zeolite, silica, glass