What is the difference between limestone and marble?

Is limestone the same as marble?

No, though they are related. Wikipedia says that in geology the term marble refers to metamorphosed limestone, but that its use in stonemasonry is broader and includes unmetamorphosed limestone. So a stone sold as marble may be a true recrystallized marble or an unmetamorphosed limestone.

That is why we suggest asking for the stone name and the ASTM classification of the block, and judging a sample. The classes differ, as the table shows.

How do limestone and marble compare on density and absorption?

High-density limestone can approach marble on density and compressive strength. It still allows 3% absorption against 0.20%, about fifteen times more. For a tub or basin that sits wet, that gap is the figure to weigh.

Which absorbs more water, limestone or marble?

Limestone, in general. ASTM C503 caps calcite marble at 0.20% absorption by weight, while ASTM C568 allows 12% for low-density limestone, 7.5% for medium and 3% for high. Great Floors describes the honed or textured limestone sold today as very absorbent and susceptible to staining, and recommends a sealer.

Marble is not waterproof. The same guide says marble stains and abrades because of its softness, and that honed marble is very absorbent and should be sealed.

Do limestone and marble both stain and etch?

Yes. Both are calcium carbonate, so acids dissolve the surface and leave dull etch marks, most visibly on a polished face. Wikipedia notes that calcite and aragonite sit below 4 on the Mohs scale and that limestone fizzes in dilute hydrochloric acid. Great Floors says acidic food, drink and cleaners etch marble.

Stain risk follows absorption, so limestone stains more readily, and sealing lowers staining on both stones. Sealing does not prevent etching. Use a stone cleaner, rinse after use and wipe up acidic products quickly. The care guide has the routine.

How do they look and feel different?

Marble's character comes from veins and swirls, created by clay, sand, iron oxides or chert in the original limestone that recrystallized with it. Limestone is commonly white to gray, with iron or manganese giving off-white, yellow or red tones, and its interest is in grain, fossils and quiet tonal change.

Thermal conductivity differs too. Engineering ToolBox lists marble at 2.08–2.94 W/m·K and limestone at 1.26–1.33, so limestone conducts heat away somewhat more slowly. For how thick stone behaves with bath water, see do stone bathtubs keep water warm.

Which one should you choose for a bathtub or basin?

Choose marble for low absorption, a polish and distinctive veining. Choose limestone for a calm, matte face, if you accept more sealing and a higher stain risk. Pietra Fonte's range includes marble and travertine, which is a spring-formed limestone. Plain limestone is not in our current range.

A marble tub weighs a little more than a limestone one of the same size, since we use about 168 lb/ft³ for marble against about 150 for limestone. The weight guide has the full figures. Check floor support with a structural engineer. For the nearest limestone-family option, see travertine vs marble.