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The Erin Limekilns: A Business From Burning Rocks

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Hidden : 11/1/2015
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Geocache Description:

For this earthcache you will learn how quicklime was produced from limestone, find out the many uses for it, and you will see where quicklime was made in a few of the famous limekilns of Houston County.  You may find it amazing that a business can be made out of burning rocks...


Since the early times of civilization, lime has been widely used for many purposes.   One form is called quicklime or burnt lime, and it is produced by heating formations that contain calcium carbonate ( CaCO3), such as limestone or seashells.   When heat of over 1,517 °F is applied to it, decomposition of the calcium carbonate will produce calcium oxide (quicklime) with a release of carbon dioxide:
CaCO3 + heat → CaO + CO2
The resulting quicklime is white, caustic (corrosive to other materials, including living tissue), and alkaline.  It is also not stable in this form, and over time it will react with carbon dioxide (CO2) in the air to revert back to its original CaCO3.


Quicklime was discovered long ago to be useful for a multitude of purposes. It is a key ingredient of plaster, whitewash, soap and some types of fertilizer.  It can also be used for water purification.  A few other interesting uses are: 
Heat - When hydrated, thermal energy is produced.  This can be used as a source of portable heat, as used in self-heating cans to warm the food contained inside.
Light - When heated to temperatures above  4,350° F, it will emit a glow.  This is where the term limelight comes from, and the "limelight effect" was used in theatrical productions beginning in 1836. Limelight continued to be used until electrical light was invented, but the term referring to someone as being "in the limelight" continues today.
Mortar - When mixed with water, slaked lime is produced.  When the water evaporates and the lime reacts with the carbon dioxide in the air, it will set as a non-hydraulic cement.
Disease control- Because quicklime is so caustic, it is used in disaster zones to speed up the disintegration of dead bodies to prevent the spread of infection.


To create the heat necessary to break down sources of calcium carbonate (such as limestone), special structures known as limekilns have been used over the centuries.
A limekiln contained a bowl-shaped burning chamber that had a brick inlet at the bottom (the "eye") which would provide air for its fire. Grate bars would be constructed across this eye and then the limestone and fuel (wood or coal) would be placed on top of these bars in successive layers:
Image is in the public domain 

The size of the limestone lumps loaded into the kiln was very important.  Typically the ideal size were lumps from 1 inch to 2.5 inches.  This size allowed air to pass through the layers so the fire could breathe during the burning.  However, if the lumps were too large then full decomposition into quicklime would not take place.  The remaining unburned limestone could then collapse downward and extinguish the fire.  Because of these limits, limekilns were restricted in their dimensions and this is why you find them all roughly the same size.
After the burning was completed and the kiln was cool, the lime could be raked out of the base and separated from ash and other "riddlings."
The normal turnaround time to produce a load of quicklime from a limekiln was 1 week. One day was needed to load the kiln, and then 3 days were used for burning.  After 2 more days of cooling, one last day was used to unload the quicklime.  A single kiln could produce around 30 tons of quicklime in a single burning.


Because quicklime can be created from heating limestone, Tennessee had many potential locations for creating quicklime due to its abundance of sedimentary limestone throughout the state.  Houston County was an ideal location due to the high quality of limestone that was discovered in its hills.
The limekilns were built in this area during the 1870s.  The lime industry in Erin and Houston County flourished for years until the 1940s.  Five of these limekilns can still be seen today, and for this earthcache you will visit two of the locations.
The Erin Limekilns (the "Double Stack") are located at the coordinates for this earthcache.  Another nearby kiln you will need to visit is the Quarry Limekiln, and it is located across the street next to the Mexican restaurant at the following coordinates:
36 19.010'
087 42.731'
At the Quarry Limekiln, the cave across the small lake is man-made.  The cave and the now-flooded quarry was formed by the excavation of limestone for the kilns.  The quarry became flooded when the limestone workers intersected a spring.  Local legend maintained that the water filled the area so fast that the work crew had to leave their equipment behind, and it is still under the water.  However, scuba divers in 2013 found no made-made structures or objects left from the quarry operation.


Provide your answers to the following questions in an email sent to me.  Do not provide them in the logs.  If any logs do not have the answers sent to me, the log will be deleted.  
  • Look closely at the rock used by the masons to create the limekilns, both outside and inside through one of the openings.  The better kiln to examine may be the Quarry Limekiln for this question.  Describe the rock used for the exterior and interior of the kilns.  Why do you think it was important to use 2 different types in its construction?
  • From information provided at the Double Stack location, what was the purity of the quicklime produced here from the high-quality limestone?
  • What was the primary use throughout the United States for the quicklime produced here?
  • The quicklime industry in the area stopped in the early 1940's for what geologic reason?
  • Estimate the size of the man-made cave entrance quarried from the limestone that is across the lake from the Quarry Limekiln and provide your estimate.
  • (OPTIONAL) Upload a picture of yourself and your GPS at one or both of the limekilns.  Be sure to not show anything in the picture that would provide answers to the questions.

Congrats to momndad2boys for the FTF on this earthcache!

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