Sedimentary rocks (2)

Identify this Sedimentary Rock 22cm Reacts with dilute hydrochloric acid Comprises over 70% broken bivalve shells Remainder of rock is silt and iron oxides... Identify this Sedimentary R

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Sedimentary Rocks

A Virtual Practical

I.G.Kenyon

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The following slides are all

sedimentary rocks From the information displayed

Decide if the rock is:

clastic, organic or chemical

Identify each rock as

accurately as possible Suggest a sedimentary environment

in which it may have formed

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Identify this Sedimentary Rock 1

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2cm

Reacts with dilute hydrochloric acid

Comprises over 70% broken bivalve shells

Remainder of rock is silt and iron oxides

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2cm

Comprises entirely clay minerals and carbonaceous material

Well preserved graptolites are found in the rock

Splits into thin layers easily (Fissile)

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1cm

Reacts with dilute hydrochloric acid Comprises entirely of spherical grains 0.5–1.0mm in diameter

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4cm

Comprises angular fragments 0.5mm – 8cm in diameter All parts of the rock react with dilute hydrochloric acid

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Comprises mainly sub angular quartz and feldspar grains

20% of the rock has fragments 2 - 4mm in diameter

5mm

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1cm

Fibrous appearance

Very low density

Clearly visible remains

of organic matter

Rich in carbon

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2cm

Composed entirely of silica Broken surfaces show conchoidal fracture

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Comprises some clay minerals such as kaolinite and illite

Has a gritty feel when rubbed on the teeth, >10% quartz present

1cm

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Well rounded flint pebbles 8mm – 6cm in diameter Cement does not react with dilute hydrochloric acid

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Rich in carbon, makes a black mark on paper

No recognisable traces of organic material evident

1cm

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Comprises almost entirely clay minerals, chiefly kaolinite

No bedding or laminations evident Plastic when wet

1cm

Grain size <1/256mm

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Comprises well rounded quartz grains 0.25 – 0.5mm in diameter

Weak iron oxide cement-crumbles in the fingers (friable)

1cm

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Reacts with dilute hydrochloric acid

Rock is made up of coccoliths

Fossil replaced

by flint

2cm

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Reacts with dilute hydrochloric acid Made up mainly of broken crinoid stems

1cm

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Comprises entirely well rounded quartz grains 0.25–0.75mm in diameter

Very well cemented together by silica

1cm

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Reacts with dilute hydrochloric acid Comprises angular fragments 0.5mm – 5cm in diameter

1cm

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1cm

Comprises angular to sub angular grains of quartz and feldspar

Contains more than

25% feldspar

Iron oxide cement

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All particles are angular

Red iron oxide cement

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1cm

Comprises quartz and muscovite grains

Splits readily into slabs 3-6cm thick

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Reacts with dilute hydrochloic acid Made up entirely of angular shell fragments 0.5-3mm

1cm

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Has a woody ‘ring’

to it when tapped

Rich in carbon

Low density

Organic structure clearly visible

1cm

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Made up entirely of hydrated calcium sulphate

This variety is called Desert Rose

2cm

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Contains some clay minerals, chiefly kaolinite

Over 10% quartz present plus mica flakes Feels gritty when rubbed on the teeth

Mica flakes concentrated on lamination surfaces

1cm

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Jet black colour

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Made up entirely of clay minerals, chiefly kaolinite

No obvious laminations or bedding present

Contains well preserved trilobite pygydium

2cm

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2cm

Reacts with dilute hydrochloric acid Has an internal concentric banded structure Specimen obtained from the roof of a limestone cave

2cm

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Majority of clasts are rounded to well rounded Poorly sorted, grain size varies <1mm to 10cm

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1cm

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1cm

All parts of the rock react with dilute hydrochloric acid Comprises shell fragments, faecal pellets and large ooliths

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Comprised of clay minerals and carbonaceous material

Lacks distinct laminations Contains well preserved plant fragment

1cm

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Comprises mainly quartz grains <0.25 in diameter

Brown colour due to 10-15% clay content Contains external moulds and casts of brachiopods

1cm

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Some rock fragments

Poorly sorted, particle

size ranges from

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Rich in iron, hence brownish colour (limonite) Cannot be found forming anywhere on earth today

1cm

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Name this Sedimentary Rock 36

Reacts with dilute hydrochloric acid Contains corals preserved

in life position

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1cm

Mixture of rock fragments and quartz grains 0.5mm to 5mm in diameter Matrix consists of mud and silt and makes up over 20% of the rock

Locally known as Haggis Rock

Sub-angular to sub-rounded particles

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1cm

Particle size 1mm up to 8mm, quite poorly sorted Mineralogy mainly sub-angular to sub-rounded quartz and feldspar

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Reacts with dilute hydrochloric acid May contain a small

percentage of clay minerals

1cm

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1cm

Comprises quartz grains 0.25 – 0.75mm in diameter

Moderately well cemented by glauconite, a pale green mineral

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Answers 1.

1 Greywacke 11 Conglomerate

2 Bioclastic Limestone 12 Bituminous Coal

3 Black Shale 13 Clay

4 Oolitic Limestone 14 Desert Sandstone

5 Mudstone 15 Chalk

6 Limestone Breccia 16 Crinoidal Limestone

7 Millstone Grit 17 Orthoquartzite

8 Peat 18 Limestone Breccia

9 Flint 19 Arkose

10 Siltstone 20 Breccia

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Answers 2.

21 Micaceous Sandstone 31 Biochemical Lst

22 Calcareous sandstone 32 Mudstone

23 Lignite(Brown Coal) 33 Fine Sandstone

24 Rock Gypsum 34 Conglomerate

25 Micaceous Siltstone 35 Ironstone

26 Anthracite 36 Coral Limestone

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The End

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