Chalk vs. Limestone — What's the Difference?

A soft, white limestone used for writing and drawing.

A sedimentary rock mainly composed of calcite.

Serves as a natural water filter in aquifers.

Varies in color and hardness.

Found in specific marine environments.

Used extensively in construction and industry.

Forms from marine organism remains.

Forms in diverse environments.

Used in agriculture to improve soil.

Supports karst topographies with unique ecosystems.

Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton which had fallen to the sea floor. Chalk is common throughout Western Europe, where deposits underlie parts of France, and steep cliffs are often seen where they meet the sea in places such as the Dover cliffs on the Kent coast of the English Channel.

Limestone is a common type of carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).

A white soft earthy limestone (calcium carbonate) formed from the skeletal remains of sea creatures.

A common sedimentary rock consisting mostly of calcium carbonate, CaCO3, used as a building stone and in the manufacture of lime, carbon dioxide, and cement.

Short for French chalk

An abundant rock of marine and fresh-water sediments; primarily composed of calcite (CaCO₃); it occurs in a variety of forms, both crystalline and amorphous.

Write or draw with chalk

Pertaining to or made of limestone.

Charge (drinks bought in a pub or bar) to a person's account

A rock consisting chiefly of calcium carbonate or carbonate of lime. It sometimes contains also magnesium carbonate, and is then called magnesian or dolomitic limestone. Crystalline limestone is called marble.

A soft compact calcite, CaCO3, with varying amounts of silica, quartz, feldspar, or other mineral impurities, generally gray-white or yellow-white and derived chiefly from fossil seashells.

A sedimentary rock consisting mainly of calcium that was deposited by the remains of marine animals

A piece of chalk or chalklike substance in crayon form, used for marking on a blackboard or other surface.

(Games) A small cube of chalk used in rubbing the tip of a billiard or pool cue to increase its friction with the cue ball.

A mark made with chalk.

Chiefly British A score or tally.

To mark, draw, or write with chalk

To rub or cover with chalk, as the tip of a billiard cue.

To make pale; whiten.

To treat (soil, for example) with chalk.

(uncountable) A soft, white, powdery limestone (calcium carbonate, CaCO3).

(countable) A piece of chalk, or nowadays processed compressed gypsum (calcium sulfate, CaSO4), that is used for drawing and for writing on a blackboard (chalkboard).

Tailor's chalk.

A white powdery substance used to prevent hands slipping from holds when climbing, or losing grip in weight-lifting or gymnastics, sometimes but not always limestone-chalk, often magnesium carbonate (MgCO3).

A platoon-sized group of airborne soldiers.

The favorite in a sporting event.

The prediction that there will be no upsets, and the favored competitor will win.

To apply chalk to anything, such as the tip of a billiard cue.

To record something, as on a blackboard, using chalk.

To use powdered chalk to mark the lines on a playing field.

(figuratively) To record a score or event, as if on a chalkboard.

To manure (land) with chalk.

To make white, as if with chalk; to make pale; to bleach.

A soft, earthy substance, of a white, grayish, or yellowish white color, consisting of calcium carbonate, and having the same composition as common limestone.

Finely prepared chalk, used as a drawing implement; also, by extension, a compound, as of clay and black lead, or the like, used in the same manner. See Crayon.

To rub or mark with chalk.

To manure with chalk, as land.

To make white, as with chalk; to make pale; to bleach.

A soft whitish calcite

A pure flat white with little reflectance

Amphetamine used in the form of a crystalline hydrochloride; used as a stimulant to the nervous system and as an appetite suppressant

A piece of chalk (or similar substance) used for writing on blackboards or other surfaces

Write, draw, or trace with chalk

Yes, they can coexist in regions where sedimentary layers of different compositions are present.

No, it also finds applications in agriculture and art, among other uses.

Chalk is softer and typically white, formed from marine organisms, unlike other limestone types.

Not all, but limestone is especially susceptible to erosion that forms caves and karst landscapes.

No, it forms over geological timescales, making it non-renewable.

Chalk forms in deep marine conditions from the accumulation of microorganism shells, unlike other limestone types.

It can adjust soil pH, improving fertility and crop yields.

Yes, depending on its mineral content, limestone can range from white to black.

Its durability and versatility make it suitable for various construction materials.

Limestone's solubility in water leads to the formation of karst features like caves and sinkholes.

Yes, both are primarily composed of calcite.

Both are sedimentary rocks, but chalk specifically forms from the calcite shells of marine organisms.

Yes, it can naturally filter water, improving its quality.

Yes, due to its softness, chalk is easier to carve than harder limestone varieties.

It's used to reduce soil acidity, benefiting plant growth.