Lime comes from limestone rock and serves as a popular soil stabilizer with many applications. You can use it for everything from growing vegetables to making cement!
We’ll cover the basics about limestone and lime, including:
Limestone is a porous, sedimentary rock that forms through chemical and biological processes (more on those soon). It has a grainy texture and is usually white; it can also be gray, brown, yellow, black, or blue.
Limestone rock is at least 50% calcium carbonate (CaCO3).1 Calcium carbonate’s mineral structure can be calcite or aragonite. Dolomite limestone contains high amounts of magnesium carbonate. Much like carbonated soda, carbonates in limestone “fizz” in acid.
Calcium carbonate often comes from fossilized animals, plants, and shells. While some varieties contain large fossils, microcrystalline limestone grains are less than 0.001 millimeters wide.2
Finally, limestone contains other particles like clay, quartz, or silica.
Limestone forms near Earth’s surface over many eons. Usually, detritus and eroded rock particles pile up. Then, other rocks or water compact them while calcium carbonate cements them together. Gradually, this sediment turns to stone in a process called lithification.
Typically, limestone forms in clear, warm, shallow water with many organisms and shells. However, sometimes it forms when water drips or evaporates, leaving mineral deposits behind. Cave features like stalactites and stalagmites develop this way.
Fun fact: If you touch cave formations, your skin’s oils counteract the minerals and make them stop growing. So, look but don’t touch!
Limestone is common in areas that used to be seas. The central U.S. is a major limestone producer, along with Mexico, Brazil, Belgium, Germany, Italy, Poland, Russia, China, Japan, and India. Today, limestone deposits are forming in the Caribbean Sea, Gulf of Mexico, and Persian Gulf, as well as around Indonesian and Pacific islands.3
Limestone rock comes in many varieties:
When geological events put immense pressure on limestone, it turns into marble. And when limestone dissolves, it forms karst topography that’s prone to caves and sinkholes.
Fun fact: As coral, fish, and other sea-dwellers die, their remains lithify into limestone that helps form coral reefs.
In 2007, the U.S. produced about 1.1 billion metric tons of limestone and imported 20 million more.4 People use limestone rock for many projects:
The Empire State Building, Metropolitan Museum of Art, and Washington National Cathedral all contain limestone from Indiana, a state whose first commercial limestone quarry opened in 1827.5 Limestone is popular for construction because it’s soft enough to carve into the shapes people want, yet strong enough to last for years. Plus, its color variations work for any project.
Scientists also study limestone to better understand Earth’s geological timeline, thanks to the fossils embedded in it. However, one use is more common than all of these: crushing.
Most limestone rock is crushed into aggregate. Almost every construction project requires some type of aggregate, and since the U.S. has large limestone deposits, it’s logical to use what we have! Limestone accounts for around 70% of U.S.-made crushed rock, and most imported limestone is pre-crushed for easier transport.6
Crushed limestone is used for road construction, building foundations, cement-making, and other projects that don’t need extremely strong, large rocks to bear loads.
People use limestone because it’s effective, but it has some pitfalls. Acids dissolve and discolor it. Because it’s porous, it’s prone to weathering, erosion, and rising damp. And because it’s soft, it’s prone to flaking, crumbling, and chipping that make it unsuitable for certain projects.
You may hear people use limestone and lime interchangeably, but they’re quite different. Limestone is the parent rock, primarily made of calcium carbonate. Lime is calcium oxide. It’s made from limestone that people break down and chemically process.
In 2021, U.S. companies produced over 17 million tons of lime.7 So, how’d they do it?
First, engineers test limestone’s chemical composition. If it will make good calcium oxide, miners harvest the rock from underground or surface quarries. They crush it into smaller chunks for transportation to the production plant.
At the plant, equipment operators use front-end loaders to put crushed limestone into a hopper. From there, a conveyor belt feeds it into a secondary crusher that pulverizes the limestone even smaller. The pieces need to be uniform to produce consistent lime, so a screening plant sorts the crushed limestone by size. It sends poorly sized pieces to a reject hopper, while a buffer hopper delivers acceptable pieces to the kiln.
Several kiln types exist—such as shaft kilns and rotary kilns—and each type heats the crushed limestone to temperatures ranging from 1,650°F to 2,000°F. This intense heat releases carbon dioxide from the limestone, leaving behind purified lime in a process called calcination.
The two main types of lime many industries use are quicklime and hydrated lime.
Quicklime, also called burnt lime, is calcium oxide that results from calcinating limestone rock. It contains one calcium atom and one oxygen atom.
It’s very absorbent; it can even absorb carbon dioxide from the air. When it absorbs rain or groundwater, it releases heat and bubbles that make it look alive. That’s where the name comes from: quick means living. Some portable heaters use quicklime-water reactions.
You can categorize types of quicklime by size:
You can also categorize quicklime by its magnesium carbonate content. High-calcium lime contains less than 5% magnesium carbonate, magnesian quicklime 5-35%, and dolomitic quicklime 36% or more.9
You may also hear about lime kiln dust. While technically a lime-making byproduct and therefore less effective, it can help dry soil at construction sites.
Hydrated lime is quicklime with water added, so its chemical name is calcium hydroxide. However, hydrated lime is usually a fine, dry powder. The water stays inside the calcium oxide particles—just like your body’s cells contain water but are solid rather than liquid.
Powdered hydrated lime is less dense than quicklime, and its particles are smaller than lime fines.10,11 Hydrated lime with extra water is called slaked lime. And when you suspend hydrated lime in water, that’s quicklime slurry.
Lime serves numerous purposes in construction, agriculture, soil stabilization, environmental remediation, water treatment, mining, and manufacturing. According to the U.S. Geological Survey, 90% of lime goes toward industrial and chemical uses.12
Fun fact: Fame is called “the limelight” because in the 1800s, theaters heated blocks of quicklime to make stage lighting.13
People have used quicklime in construction dating back to 4,000 B.C., when the ancient Egyptians used it in the pyramids. Ancient Greeks and Romans also used quicklime.
Today, we use quicklime to dry soil at construction sites, which reduces downtime and shortening project timelines. Bonding and paving materials such as plaster, cement, and asphalt all contain hydrated lime.
Adding lime to soil changes its pH to be more alkaline, or less acidic. Farmers do this because many plants grow better in alkaline soils.
Aglime refers to any lime for agricultural use, from large-scale industrial farming to home gardening. People also call it agricultural limestone or garden lime. Many people use limestone and lime interchangeably when referring to aglime. But since you now know that limestone and lime are different, it’s important to check that you have the right product and know how much to use.
Lime fines are great for stabilizing soil because they quickly dry and harden it. Contractors use lime to strengthen weak soils and improve their load-bearing capacity.
In roadbuilding, lime stabilizes and hardens the subbase to allow for thinner pavement, which saves time and money. Additionally, a lime-stabilized subbase can increase the road’s lifespan, reduce maintenance costs, and—most importantly—keep drivers safe.
Lime helps dry chemical spills and contaminated water at industrial sites or landfills. Mechanics use it to clean up oil and antifreeze spills in their shops. And water treatment plants use lime to adjust the pH balance, killing harmful microorganisms so we have safe drinking water.14
Ironically, lime dust keeps down mine dust. So, miners have fewer health risks, and it helps prevent coal dust from overheating and exploding. Lime also helps manage mine waste products like slurry, tailings, and acid drainage.
Manufacturers use lime in numerous products:
We use lime for many products and processes that keep us safe. But on the flip side, overusing limestone or especially lime can be hazardous.
Lime and limestone dust can severely irritate eyes, skin, and lungs. In fact, armies from in the Middle Ages may have thrown quicklime on their opponents, hoping these irritations would inhibit their fighting.18 Overexposure to lime can lead to silicosis and cancer.19 When using lime, wear protective gear like safety glasses, long sleeves, and respirators.
Improperly or excessively using limestone and lime can also negatively affect the environment. Limestone dust pollution may reduce plants’ ability to process sunlight and water.20 Too much lime can make soil too alkaline, so crops won’t grow. And it can add too much calcium to water, which harms plants, plumbing pipes, and people.
Essentially, lime and limestone are like most things in life: they’re very useful, they can be dangerous if misused, and it’s smart to know the risks so you can stay safe.
There you have it: lime is a chemical product that people derive from limestone rock. Both lime and limestone come in many varieties, and it’s truly amazing how many ways we use them.
So, whether you’re admiring a limestone monument, driving on a road near your home, or eating a sugary treat, remember to be grateful for all the ways people have learned to use limestone and lime throughout history!