Sedimentary Rock

In clastic (or detrital) sedimentary rock:

1. Weathering of an existing body of igneous, metamorphic, or sedimentary rock by natural mechanical or chemical means.
2. Erosion of the weathered particles by wind, water, ice, and gravity.
3. Deposition of the particles after transportation.
4. Compaction of the particles by the weight of overlying sediments.
5. Cementation of the particles by mineral precipitation from surrounding fluids.

Sedimentary rocks have been on the earth since it first cooled enough to form a solid crust. Since then the processes of weathering and erosion have lead to the deposition of sediments. The oldest sedimentary rocks we have been able to identify are found in Greenland and are about 3.9 billion years old.

The recognition as to what sedimentary rocks were and how they were formed came with the emergence of the science of Geology and the first geological maps (made by William Smith in England) in 1799. The understanding as to what sedimentary rocks were came as part of the principle of uniformitarianism which was developed from the work of the Scottish geologist James Hutton in 1785.

limestone is composed of various minerals (a material made up of a combination of atoms of various elements arranged in a specific atomic lattice to form crystals - as they are a mixture of varying elements they may also be referred to as compounds). The most common of which in Limestone is Calcite / Calcium Carbonate.

Calcium Carbonate has the chemical formula CaCO3. From this we can see that limestone is formed predominantly from the elements Calcium (Ca), Carbon (C) and Oxygen (O).

A type of limestone known as dolomite is composed of calcium magnesium carbonate CaMg(CO3)2 .

The density of limestone is very variable as it is a natural earth material. As such, a range of densities are quoted in the literature and testing should be done on a specific sample to get an exact result.

Range of intact densities for limestone:

Common - 2100 to 2610 kg/m3[A] and occasionally up to 2900 kg/m3[B]

In imperial units:

131.1 lbs/ft3 to 162.9 lbs/ft3 and occasionally up to 181.0 lbs/ft3.

Intact Limestone can have a Young's modulus (E) ranging from:

9 GPa - 80 GPa.A,B

Poisson's ratio (v) for intact specimens varies from between:

0.2 - 0.3.B

Bulk modulus (K) derived from the above values using the following relation:

K = E / (3(1-(2v))

Bulk Modulus ranges from:

5 GPa - 66.67 GPa

Shear modulus (G) derived from the above values using the following relation:

G = E / 2(1+v)

Shear modulus ranges from:

3.5 GPa to 33.33 GPa

Intact Limestone can have a uniaxial compressive strength ranging from:

15 MPa - 290 MPa.A,B

Sources:

[A] Bell, F. G. (2007). Basic Environmental and Engineering Geology. Dunbeath, Whittles Publishing Limited.

[B] Cobb, F. (2009). Structural Engineer's Pocket Book, Second edition. London, Butterworth-Heinemann.

Sedimentary rocks can be formed in various ways, and are classified by the method of formation or content. Broadly, sedimentary rock is classified as being clastic, organic, or chemical. Following are the three types and how they are formed.

Clastic sedimentary rock:

The majority of sedimentary rock on Earth is formed from particles of pre-existing rocks. This route begins with the weathering and erosion of sedimentary, igneous, or metamorphic rocks. Through these processes, larger rock is broken up into smaller particles which are transported by moving water, ice, gravity or wind, and deposited at the bottom of a lake, a river delta, an ocean, or similar location where further movement is restricted or slowed down. The rock particles can range in size from boulders to clay particles less than .002 mm in diameter. If these rock particles are covered by additional particles, eventually the weight from above will start the process of lithification. Lithification is the compaction and cementing together of sediment particles which form rock. Compaction squeezes out the fluids and space that exist between the particles, and cementation results when minerals form from the migrating solution. Once cementation occurs, the new sedimentary rock has been formed. Rocks formed in this manner include sandstone, shale, mudstone, breccia, and conglomerate.

Organic sedimentary rock:

Chalk and other fossiliferous limestones are composed of the skeletons of marine organisms. Coal is composed of vegetation that originated and was deposited in swampy and marshy waterlogged soils which prevented their full decay after their death. As their remains piled up and were covered by more and more deposits, they were compacted and cemented in the same manner as clastic rock.

Chemical sedimentary rock:

Sedimentary rock can also form when minerals in a body of water have so saturated the water that they precipitate out, like a cloud that is so full of moisture that it pours out rain. Some limestones are formed in this manner as the mineral calcite precipitates out of a saturated solution and undergoes the process of compaction and cementation. The supersaturated solutions can also be caused by evaporation of a body of water high in mineral solution content. As the water evaporates, the mineral percentage of the remaining solution becomes higher and higher, until the mineral crystallizes. Rocks such as rock salt and rock gypsum are formed in this manner.

It is formed by the sedimentation of material at the Earth's surface and also in the bodies of water.
Sedimentary rocks are formed at the bottom of lakes after being compressed over a long period of time...
Sedimentary rocks are formed mainly through a proccess called Diagnesis. Diagnesis can be defined as the combined process of gradual and contineous accumulation, stratification, compactation, sedimentation, cementation, and lithification of transported and deposited debrises, detrituses, regoliths and other earths disintegrated materials, to form sedimentary rocks over a long period of time. Sedimentary rocks are created or formed out of virtually anything that exists around, which can be moved either by wind, water, glacier or waves and deposited in a specific place over and over again. They are rocks that tends to "germinate" by addition of materials/matter in stratas/layers and then the materials hardens, glues up/cements to themselves and hardens with time.
Sand and other particles are buried, compacted, and cemented together.

If you have access to soil / dirt, get about a cup. If you can't get soil / dirt, you can buy a box of Baking Soda for 0.50 to $1.00 per pound box. Get an old small box and old newspapers. You can also get a tall black garbage bag, and cut it so you can open it up completely. Lastly, get a half cup of cool-cold water, and an eyedropper or teaspoon.

Lay the garbage bag on the floor to protect the rug/floor. Lay a couple sheets of an open newspaper in the middle; save the rest. Next, put your open small box on the newspaper.

Sedimentary rock is typically composed of sand. But explain to the child that it can take millions of years for sand to compress to make rock. So, we''re going to try with either dirt, or baking soda. I think Baking Soda will harden faster so try it first.

Put a thin layer of baking soda in the box -- just a couple inches long and a couple inches wide. Carefully add a verysmall amount of water across the soda, just to make it wet. Important to just use a small amount of water! You can use a Popsicle stick to mix it, or a knife, or even your finger.

Now, take another sheet of newspaper and fold it so it fits over the Soda mixture. PRESS down on the soda, REALLY hard. Explain that this pressure is what happens to sands and sand mixed with soil, which comes from rocks eroding.

You can put a lamp (100 watt bulb) above the mix and let it dry. Check in 30 minutes, and 1 hour, to see how much it has dried. Leave the newspaper square on top... add a new layer of Baking Soda and another small amount of water... and again, PRESS down. Let that layer dry.

Explain that water moves dirt particles from rocks, moving the dirt down hills and down streams, etc. Each layer adds pressure from above/top, which presses out the water. After many thousands of years, the grains of sand/dirt become stuck together and don't move as much when water comes across it. More & more layers get added, but they aren't all neat and even. After millions of years, there's been a lot of pressure and many hundreds of layers. If you could cut the rock, you would see layers with a mixture of colors-- tan, red, yellow, etc, depending on what elements were in the particles.

Looking at the Baking Soda "rock", it is likely crumbly. It breaks apart easily with only 2 layers. If you move a piece of it and add water, the material would easily "run"--- it has not dried for millions of years as more layers got added. The piece you moved will not go back into the rest of it and cling together again right away--- it would again need time and pressure.

*If you try the dirt, it will likely not cling together as easily. It would need days to dry.