Sedimentary Rocks

 Miracosta College
Sedimentary rocks are classified in a variety of ways:
1) by sediment clast size
2) by mineral composition
3) by their origin:
  • Lithogenous or terrigenous sedimentary rocks have formed from sediment that was primarily consisted of small fragments of preexisting rocks that have made their way to a final depositional setting. They have since undergone lithification (involving compaction and cementation).
  • Biogenous sedimentary rocks have formed from living organisms, consisting of fragments of shell, bone, teeth, wood, microscopic skeletal remains, excerement, or other organic matter. These material can be preserved or undergo alteration or mineral replacement as they undergo lithification.
  • Hydrogenous sedimentary rocks are rocks made up of minerals that have precipitated directly from water. This involves changes in the temperature and chemical composition of the fluid precipitating the mineral components.
  • Cosmogenous sedimentary rocks consists of material that has come in from outer space: cosmic dust or meteoritic material. By comparison, this material is rare or a trace component in sedimentary rocks.
  • A mix of the above components: Many sedimentary rocks fall into mixed categories (examples below). For instance, the cement that holds sedimentary particles together is typically precipitated or recrystallized in the presence of water. Carbonate sedimentary rocks have their own classification based on their biological and chemical components.
4) by unique characteristics of the sedimentary environment or setting in which they formed, or a mix of some or all of the above.

Click on images for a larger view.

Lithogenous Sedimentary Rocks

brown conglomerate rock with white pebbles
Conglomerate 8 		conglomerate rock with multicolored rock fragments
Conglomerate35		 A multi-colored cobble of conglomerate that looks similar to concrete, but containts a mix of colored pebbles.
Conglomerate 49		 red sandstone
Arkose sandstone 13 		Lithic Sandstone
Lithic Sandstone 46
white sandstone with crossbedded layers
Quartz sandstone29		 greenish brown sandstone
Graywacke sandstone 45		 A brown, medium-to-coarse grained graywacke sandstone.
Graywacke sandstone 48
Tuffaceous sandstone 50		 tourquise blue sandstone
Sandstone copper ore 28
a stack of 5 rounded ball-shaped concretions.
Sandstone concretions 27		 sandstone slab displaying ripple marks
Sandstone with ripples 32		 sandstone slab displaying ripple marks
Sandstone with ripples 34		 tan colored rock with faint brown stripes
Siltstone 33		 gray rock with alternating gray and yellow layers
Siliceous mudstone 24

Biogenous Sedimentary Rocks

Lump of coal like you would expect for Christmas
Bituminous coal 7		 rock displaying bark detail preserved on outer surface
Fossil wood from Ohio 10		 rock displaying bark detail preserved on outer surface
Fossil wood from Arizona 11		 rock displaying red and black alternating layers
Banded iron formation 3		 rock displaying alternating black and white layers
Porcellanite (shale) 25
rock display alternating layers of red, orange, an brown
Chert 43		 rock showing red layers
Radiolarian chert 5		 conglomeratic rock display a variety of clasts of different colors in a white matrix
Chert pebble conglomerate 4		 a buff-gray chunk of limestone with an irregular surface with ripples
Limestone 21		 A folded, banded layered rock that kinda looks like a vulture (note eyeball and beak at top)
Dolostone 9
limestone rock with mounded thin layers
Limestone stromatolite 19
Stromatolitic limestone 50		 a limestone slab covered with small brachiopod shells
Limestone brachiopods 16		 limestone slab covered with branching bryozoan fragments
Limestone bryozoans 17
 limestone slab covered with small disks of crinoid stem column fragments
Limestone (ecronite) 18
Thinly banded layers of travertine with a tufa coating on top.
Travertine 47		 a massive round chunk of a fossil coral head
Limestone coral 20		 A rugose coral with crinoid stem fragments on the surface of a limestone slab
Limestone rugose coral 40		 a brown sandy rock with a mix of snail, oyster, and clam shell fragments and casts
Fossiliferous sandstone 41		 a sandy rock full of whole small sand dollars
Sandstone sand dollars 37
three whole oyster shells stuck together by gray sandstone
Sandstone with oysters 31		 a blueish gray rock full of white clam shells
Sandstone fossils 30 		a buff-colored sandy rock made up of tiny fragments of clam shells.
Marl 23		 a conglomeratic rock with clasts covered with fossil algal growths and small rounded brown pisoliths, some snail fossils
Pisolith conglomerate 44		 a brown rock full of round hole, almost like swiss cheese.
Clam-bored mudstone 6

Hydrogenous Sedimentary Rocks (and Minerals)
a single large crystal of salt (hailite)
Halite (Rock Salt) 39		 a mas of small salt crystal stuck together
Rock Salt 36		 a rock with thin alternating layers of black and white
Anhydrite 2		 a white, partially transparent rock with no internal structure
Gypsum alabaster 14 		a clear slab of gypsum selenitie with fractures and white areas
Gypsum selenite 15
alternating white and gray thin layers of agate surrounded by a brown outer rock rind.
Agate (thunder egg) 1		 A hollow white rock displaying small quartz crystals inside
Quartz geode 12
 a mass of clear and white quartz crystals Quartz crystals 42 An oval gray rock with an irregular star-like cavity in the center filled with yellow calicte crystals
Septarian nodule 38		 a rock with a shiny gray, metal like surface.
Manganese nodule 22
See Introduction to Physical Geology: Chapter 9 - Sedimentary Rocks and Processes More rocks may be added as they become available.
https://gotbooks.miracosta.edu/rocks/sedimentary_rocks.html 2/25/2022