Sedimentary Rocks

  • When mountains are first formed, they are tall and jagged like the Rocky Mountains on the west coast of North America. Over time (millions of years) mountains become old mountains like the Appalachian Mountains on the east coast of Canada and the United States. When mountains are old, they are rounded and much lower.
  • What happens in the meantime is that lots of rock gets worn away due to erosion. Rain, freeze/thaw cycle, wind and running water cause the big mountains to crumble a little bit at a time.
  • Eventually most of the broken bits of the rock end up in the streams & rivers that flow down from the mountains. These little bits of rock & sand are called sediments. When the water slows down enough, these sediments settle to the bottom of the lake or oceans they run into.
  • Over many years, layers of different rock bits settle at the bottom of lakes and oceans. Think of each layer as a page in a book. One piece of paper is not heavy. But a stack of telephone books is very heavy & would squish anything that was underneath. Over time the layers of sand and mud at the bottom of lakes & oceans turned into rocks. These are called sedimentary rocks.
  • There are 6 main kinds of sedimentary rocks depending on what the rock looks like.
    • Sandstone is a soft stone that is made when sand grains cement together. Sometimes the sandstone is deposited in layers of different colored sand.
    • Shale is clay that has been hardened and turned into rock. It often breaks apart in large flat sections.
    • Limestone is a rock that contains many fossils and is made of calcium carbonate &/or microscopic shells.
    • Gypsum, common salt or Epsom salt is found where sea water precipitates the salt as the water evaporates.
    • Conglomerate rock has rounded rocks (pebbles, boulders) cemented together in a matrix.
    • Breccia has jagged bits of rock cemented together in a matrix.
  • Some other examples of sedimentary rocks are:

Sandstone is a gritty textured, solid block of compressed sand made from quartz grains. The sand is deposited in layers. This is easy to see when the layers are different colors.

SPECIMEN: Tumbled Sandstone


CONGLOMERATE rock has rounded rocks (pebbles, boulders) cemented together in a matrix.


SPECIMEN ORIGIN: St. Joseph Island, Ontario, CANADA
When pioneers saw this rock in Northern Ontario, they thought the rounded red & brown pebbles looked like currants & raisins in a pudding. They called the rocks Puddingstone.
The brown, red & pink pebbles inside the rock are jasper which is a kind of quartz.



SPECIMEN ORIGIN: Sault Ste. Marie, Ontario, CANADA
BRECCIA has jagged (angular) bits of rock cemented together in a matrix.
Calcite Cemented Limestone Breccia


In these specimens, the calcite acts as a cement to hold together the limestone breccia.  Some of the vugs in the breccia have been infilled with calcite crystals.
Wanapitae Breccia

ORIGIN: Lake Wanapitae, Ontario, CANADA
Wanapitae breccia is distinct in its orange and black blockiness.  

  • Fossil fuels such as coal, oil and natural gas are found in sedimentary rocks.

SPECIMEN: Anthracite Coal
Anthracite Coal

This very light, shiny black piece of coal is called anthracite coal. It is cleaner to handle than bitimous coal. It feels a bit slippery. It formed through the accumulation of peat.


  • This rock is a very distinct rock with its dark red & black banding.
  • The black layers are magnetite and the red layers are chert.

ORIGIN: Sherman Mine, Temagami, Ontario, CANADA





DESCRIPTION: This rock is a very distinct rock with its dark red & black banding. The magnetite is strongly magnetic. This specimen has been cut but not polished.
COLOR(S): burgundy-red, dark gray-black COLOR DISTRIBUTION: layers





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