Sedimentary Rock Flashcards

Conglomerate

• rounded rock fragments > 22mm

• contains obvious pebbles and larger clasts

• mix of tonnes of rocks, all different sizes

• “Cow” spots “Cowglomerate”

Sandstone

• can see with naked eye, 0.063-2mm

• sand sized grains

• feels gritty

• can be white, cream, yellow, red, brown or grey

• may show bedding / layering

• super boring

Mudstone

• grain sized <0.063mm, extremly fine-grained

  • silt and clay sized particles

• smooth or earthly appearance

• can be scratched with fingernail

• often grey, brown, red or green

• dosen’t split easily into thin sheets

• can feel soft

• dosent fizz with HCI

Limestone

• Usually light grey, cream, white, yellowish or brown

• generally fine grained, but may have fossils/grains

• soft

• REACTS WITH HCI

• can sometimes be scratched with fingernail

• can have bedding

• finer than 0.6mm

Chert

• very hard

• usually grey, white, brown, red or green

• often has a smooth, almost waxy appearance

• conchoidal fracture - curved breaks

• can look like glass

• does not react with HCI

Coal

• is king

• black or dark brown

• lighter than you expect (weight)

• can leave dust behind

• can be different stages

  • light to shiny

    • peat > lignite > brown coal > black coal > anthracite

Shale

• very fined grained

  • clay and silt sized particles

• usually grey, black, brown or reddish

• can be scratched with fingernail

• splits easily into thin sheets or plates

• often has obvious thin bedding

• can contain organic matter - called oil shale

  • dark brown/black

  • conchoidal fracture

Breccia

• made up of rock fragments, larger than > 2mm

• Clasts have sharp, angular edges

• poorly sorted - many different sizes

• fragments are cemented together by finer materials

• looks like a collection of broken rocks stuck together

Siltstone

• 0.002-0.063mm grain size, cannot see them

• feels slightly gritty

• often grey, brown, red or yellow

• may have thin bedding/layers

• generally harder and less clay-like than mudstone

Gypsum

• Very Soft

• usually white/clear

• can be scratched with fingernail

halite

• clear/white

• cubic crystals

• very soft

• salty taste