FAQ

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. 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.

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.

Limestone rock comes in many varieties:

• Caliche: “cemented” mix of calcite limestone with clay and other soils, common in arid regions

• Chalk: Soft, powdery calcite limestone made from organic and chemical matter

• Coquina: Large grains made mostly from shells and fossils

• Dolomite: Has high magnesium carbonate content

• Micrite: Starts as calcitic mud before solidifying into fine-grained rocks with white lines

• Oolite: Has small grains arranged in concentric circles

• Travertine: Forms via evaporation, especially in caves and springs with odd chemical properties

• Tufa: Forms when relatively salty water evaporates, often in arid places like Pyramid Lake

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:

• Construction

• Walls

• Decorative Trim

• Veneer and Exterior Facings

• Chalk

• Roofing Granules

• Building Stones

• Flooring

• Mine Safety Dust

• Animal Feed Filler

• Monuments

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.

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.

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.