Earth Science

Earth Materials

Sedimentary Rocks Classification

Study Tip
“Conglomerate” sounds smooth and rounded, while “breccia” has a harsher “shh” sound that makes it easy to remember as being angular.

Types of Sedimentary Rocks

Rock
Sediment Size
Other Features
Conglomerate
Large
Rounded
Breccia
Large
Angular
Sandstone
Sand-sized
Siltstone
Silt-sized; smaller than sand
Shale
Clay-sized; smallest
Study Tip
“Conglomerate” sounds smooth and rounded, while “breccia” has a harsher “shh” sound that makes it easy to remember as being angular.
Study Tip
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.

Chemical Sedimentary Rocks

  • Chemical Sedimentary Rocks: Sedimentary rocks formed by the crystallization of chemical precipitates.
  • Dissolved ions in fluids precipitate out of the fluid and settle out.
  • Sediments settle out of calmer water form horizontal layers.
  • 1st layer is deposited first & other layer is deposited on top.
  • So each layer is younger than the layer beneath it.
  • Sediments harden and the layers are preserved.

Biochemical Sedimentary Rocks

  • Biochemical Sedimentary Rock: Rocks that form from materials created by living organisms removing ions from water and falling to the bottom to become sediments.
  • Form in the ocean or a salt lake.
  • Living creatures remove ions, such as calcium, magnesium, and potassium, from the water to make shells or soft tissue.
  • When the organism dies, it sinks to the ocean floor to become biochemical sediment.
  • May then become compacted and cemented into solid rock.

Common Sedimentary Rocks Chart

Picture
Rock Name
Type of Sedimentary Rock
Conglomerate
Conglomerate
Clastic (fragments of non-organic sediments)
Breccia
Breccia
Clastic
Sandstone
Sandstone
Clastic
Siltstone
Siltstone
Clastic

Earth Science

Shale
Shale
Clastic
Rock Salt
Rock Salt
Chemical precipitate
Rock Gypsum
Rock Gypsum
Chemical precipitate
Dolostone
Dolostone
Chemical precipitate
Limestone
Limestone
Bioclastic (sediments from organic materials, or plant or animal remains)
Coal
Coal
Organic

Earth Science

Concept Check
  • What determinants are used to classify sedimentary rock?
  • What are chemical sedimentary and biochemical sedimentary? What are the differences between the two?
Supplemental Learning

Try to fill out this chart by memory:

Rock
Sediment Size
Other Features
Conglomerate
Breccia