Siliciclastic Sedimentary Rocks

Question 1

Breccia

Answer 1

Coarse grained
Angular clasts, not transported long
Mixed with finer grains in a matrix (poorly sorted)
Forms as scree, alluvial fans and wadi deposits

Question 2

Conglomerate

Answer 2

Coarse grained
Rounded clasts, transported a long time
Finer grained matrix, poorly sorted
Held in place by mineral cements
Beach and river deposits

Question 3

Orthoquartzite

Answer 3

Quartz grains only, held by quartz cement
White/grey in colour
Well sorted and rounded, transported a long time
Extensive weathering
Form in beach and shallow marine deposits

Question 4

Desert Sandstone

Answer 4

Red in colour due to iron oxide coating quartz grains
Very well sorted and rounded
High sphericity
Clasts cemented together by silica or iron minerals.
Arid environments

Question 5

Arkose

Answer 5

Medium to coarse grained
25% feldspar
Pink in colour
Moderately sorted
Sub-angular to sub-rounded, not transported long
Alluvial fan environments

Question 6

Greywacke

Answer 6

Fine and coarse grain size
Dark coloured, poorly sorted
Angular/sub-angular clasts
Turbidite deposits so show graded bedding

Question 7

Clay

Answer 7

Variety of colours, clay sized and clay minerals
Higher the organic content, darker the clay
Forms layers, distinct bedding planes

Question 8

Mudstone

Answer 8

Dark grey, very fine grained
Not layered, no plasticity
Clay minerals, mica and quartz

Question 9

Shale

Answer 9

Dark coloured, fine grained
Distinctive layers due to alignment of minerals
Fissile, easily split
Hard, brittle and impermeable

Question 10

Oolitic Limestone

Answer 10

Chemically formed
Sub-spherical sand size grains called ooliths
Micrite or spirite matrix
Tropical environments or shallow water with high energy

Question 11

Fossiliferous Limestone

Answer 11

Formed of fossils and fragments
Bioclastic
Micrite or spirite matrix

Question 12

Chalk

Answer 12

Formed from coccoliths
White due to pure CACO3
Low energy, deep water shelf environments