Sedimentary rocks

Sedimentary rocks

• Rocks that form from an accumulation of sediments derived from preexisting rocks and/or organic materials.

• These rocks form by various process that occur on or within the top few kilometers of earth’s crust

• Most sedimentary rocks are made up of solid fragments or sediments, often called “clasts”, that have been weathered or eroded from older rocks.

• Clastic texture rocks are composed of smaller rock fragments called sediments. Classified by their particle size

Pebbles, cobbles and/or boulders some silt sand or clay

Sand

Size of particles: from .0006cm to .2cm

Silt particles

Particle size: .00004 to .006 cm

Clay

Clay magnified 1,600 times

Particle size: less then .0004 cm

Cementation

• Often the clasts, such as sand, silt, and pebbles, are cemented together in a process called cementation. This happens as the sediments lose water and the dissolved minerals in the pores of the sediments forming a crystalline mineral material

Chemical sedimentary rockCrystalline Texture

• When dissolved minerals drop out of water (precipitate), they form a mass of intergrown or interconnected mineral crystals

• You can see crystals in the rock. The crystals are composed of only one mineral

Bioclastic • No crystals, No rock particles. May have shell

or shell fragments in it, or be completely black in color consisting of dead organic material

Limestone

Coal