Is Limestone Organic? (ANSWERED)

Limestone is formed from the accumulation of shells and skeletal remains of marine organisms.

These deposits are formed by either chemical deposition or biological activity.

This would suggest that limestone is organic in nature.

However, today’s definition of “organic” requires that it must contain a large percentage of carbon.

Since limestone does not contain much carbon, then it cannot be considered organic.

This article will help to explain the properties of limestone and why it may or may not be considered organic.

Is Limestone Organic? (EXPLAINED)

What is Limestone?

Limestone is a sedimentary rock which has been formed from the accumulation of shell and sand particles, as well as other organic matter, over hundreds of thousands of years.

These materials have been compressed under pressure, usually from fossils beneath them, to form a solid mass.  

The original shells and other organic matter are usually still visible as lines, circles or ovals in the rock.

Because of this distinctive layer-cake appearance, limestone is sometimes mistaken for a man-made stone, but it differs enormously from concrete because it contains no Portland cement.

Limestone is slightly porous and may allow plant roots to grow through it.

It is also slightly soluble, which means that acid rain can dissolve the calcium carbonate it contains and create cavities or pitting.

However, limestone can still be a very good building material because it is strong and durable.

It is usually white or pale grey, and can be polished to make a good-looking surface.

Some limestone contains fossils of the sea creatures that lived when it was originally made.

These fossils are visible as little round spots, circles or ovals in what look like lines running through the stone.

Limestone can be found all over the world.

In the United States, it is most commonly used as a construction material and as an aggregate for roads.

It is also mixed with cement to make concrete, which is used in buildings and sidewalks.

Limestone’s chemical qualities make it a valuable resource for the chemical industry.

Limestone is also used in the industrial process and as a flux in steel and aluminum refining.  

What Does “Organic” Mean?

At a glance, the word “organic” seems to be just a synonym for “natural” or simply another way of saying “chemical-free”, especially when referring to food.

Many foods labeled as organic are indeed free from pesticides and other harmful chemicals.

However, not everything labeled organic falls under this umbrella.

In order to qualify for use of the term organic, a food must meet certain standards.

For example, organic foods are produced without using traditional pesticides or fertilizers.

Organic livestock are required to be fed organic feed and given access to the outdoors.

In chemistry, the word “organic” is used to describe a class of molecules that contain carbon and hydrogen.

Organic molecules are generally larger and more complex than inorganic molecules (inorganic molecules contain no carbon).

Organic molecules often contain other elements such as oxygen (which contributes to the increased complexity of organic molecules) and tend to have a wider range of properties compared with inorganic molecules.

For example, most inorganic salts dissolve in water, but many organic molecules do not dissolve in water.

Thus, organic molecules have a greater capacity to form more complex and useful products.

When is Limestone Considered “Organic”?

There is a great deal of confusion about how to determine whether or not limestone is organic, and this confusion even extends into the agricultural community.

In order to have an understanding of what makes a limestone product organic, it is important to understand the process of why limestone becomes “organic” in the first place.

Limestone acts as a liming agent when it is applied to the soil.

It does this by neutralizing the pH of the soil because it contains calcium carbonate, which is a stable alkaline substance that resists changing into another substance over time.

When limestone is applied to soil with an acidic pH, it becomes “effective” in neutralizing the soil pH because the calcium carbonate reacts with the hydrogen ions (H+) and forms insoluble salts.

If a sufficient amount of calcium is added to an acidic soil, a certain percentage of that calcium will react with H+ ions and become part of the internal structure of stable compounds that are already part of the soil.

This is why some soils can require more than 100 pounds per acre of dolomitic limestone to neutralize the pH.

Limestone remains effective until it has all reacted with H+ ions to form stable compounds that cannot further change in structure over time, or until all its calcium has been tied up by its reaction with H+ ions.

Once all of the limestone has reacted, it can no longer neutralize soil acidity because it is now part of a stable compound that cannot further change in structure or be used in plant nutrition.

Several factors determine when limestone has become fully effective and how fast this will occur.

These factors include the level of soil acidity, the type of soil and its physical properties, and how long it takes for enough limestone to be added to an acidic soil so that there is a sufficient amount available to react with H+.

Limestone on its own does not provide calcium or other plant nutrients.

Calcium reacts with the H+ ions in an acidic soil and forms a stable salt, so after all of the calcium has reacted, it becomes part of a stable compound that cannot further change in structure or be used by plants.

Soil tests can measure how much limestone has been added to a particular soil and what levels of other nutrients are present.

This information is used to determine how much fertilizer is necessary for crop production, and liming materials must be added to the soil before planting so that additional limestone can neutralize the acidity caused by crop removal.

Limestone becomes “organic” after the reactions of limestone have occurred with H+ ions to form stable compounds that cannot further change in structure over time, or after the limestone has all reacted with H+ ions to form a stable salt that cannot be used by plants.


Limestone is an inorganic material. It does not fall into the category of either chemical or biological and it is considered a man-made rock that was created through natural processes.

It can be considered biogenic if there are more than 30% noncarbonate materials, and if the limestone is more than 95% calcium carbonate, then it can be considered clastic.

You might also like:

Is Limestone Organic