Limestone Landscapes

We will be delving into the, geologic characteristics of Limestones, its affects on the formation of subsurface landscapes, Tower and Cone Karsts and finally the formation of caves.

• Limestone Characteristics

Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of evaporated seas and lakes and from sea animal shells (as can be seen from the picture above). This rock is used in concrete and is an excellent building stone for humid regions. [http://www.fi.edu/fellows/fellow1/oct98/expert/limestone.htm]

Hardness:

- Relative hardness rating a H:3 on the Moh’s scale (comparable to that of a penny) http://www.rocksandminerals.com/hardness/mohs.htm

<- Sawn Limestone Block Texture

<- Weathered Limestone Texture

2. Rock Texture:
-The texture varies from coarse to fine.

-Most limestones have a granular texture.

-Their constituent grains range in size due the variation in chemical composition where limestone being a sedimentary rock has a mixture of rock components in them.

3. Rock Colour:
-Pure limestone is white or almost white.

- Because of impurities, such as clay, sand, organic remains, iron oxide and other materials, many limestones exhibit different colors, especially on weathered surfaces.

4. Chemical Composition:

- Composed largely of the mineral calcite (calcium carbonate: CaCO3).

- Limestone often contains variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules, or layers within the rock.

- The primary source of the calcite in limestone is most commonly marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze or alternatively is conglomerated in a coral reef.

- It is alkaline in nature.

5. Rock Jointing:
-Types of Rock Jointing: Presence of styolites, vertical joints and extensive bedding planes due to the processes of lithification.

6. Porosity:

- Low porosity due to the compaction of the sediments under high pressure during its formation.

7. Permeability:

- High permeability due to the bedding planes, styolites (due to iron oxide content) and vertical joints which act as avenues of weakness.

8. Specific Location:

-Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls and around hot or cold springs.

- Calcium carbonate is deposited where evaporation of the water leaves a solution that is supersaturated with chemical constituents of calcite.

- Tufa, a porous or cellular variety of travertine, is found near waterfalls.

- Coquina is a poorly consolidated limestone composed of pieces of coral or shells.


Formation of Limestones

In Layman’s Terms: For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn awayby wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

Click http://www.fi.edu/fellows/fellow1/oct98/create/sediment.htm for a simple animation.