Marble: composition, formation and properties

What is marble?

Marble is a metamorphic rock made mostly of carbonate minerals, usually calcite or dolomite. It starts out as limestone: deep in the Earth’s crust, heat and pressure make its crystals grow again into a dense, interlocking mass. The Finnish science term bank, Tieteen termipankki, gives the word two meanings. In geology, marble is this metamorphic rock. In the stone trade, it is any strong stone that takes a good polish, which brings in several other rocks as well.

In Finnish shops the word marmori also turns up in the names of vinyl floors, tiles and laminate worktops, so check the material line before you assume a product is real stone.

The key properties at a glance; each figure is explained, with its source, further down.

What is marble made of, and what is its chemical formula?

The chemical formula of marble is CaCO₃, because ordinary marble is almost entirely calcite, a form of calcium carbonate. You can read the formula like this: for every calcium atom (Ca), the stone holds one carbonate group made of one carbon atom (C) and three oxygen atoms (O₃). According to the OpenStax chemistry textbook, pearls and the shells of most molluscs are the same compound.

Marble’s other main mineral is dolomite, CaMg(CO₃)₂. Here magnesium (Mg) takes the place of every second calcium, and there are two carbonate groups. Geologist Olavi Selonen’s 2023 report on Finnish marble defines marble with more than 50% dolomite as dolomitic marble, and the Finnish Natural Stone Association (Kiviteollisuusliitto) notes that the marbles produced as dimension stone in Finland are dolomitic.

Besides these, marble usually holds small amounts of other minerals: clay minerals, micas, quartz, pyrite, iron oxides and graphite (Geology.com). They give the stone its colours and veins, but marble remains a carbonate rock. If you see marble’s composition given as a list of silica, alumina and potassium oxide (SiO₂, Al₂O₃, K₂O), the text is describing a granite-type silicate rock, not marble.

How does marble form?

Marble forms in two stages: first limestone builds up on the sea floor, then heat and pressure turn it into marble.

1. Limestone. Selonen’s report explains that limestone usually forms when shelled organisms such as mussels, snails and corals die, sink to the sea floor and harden into rock through a process called diagenesis. Limestone can also form without organisms, when calcium carbonate precipitates chemically from seawater.
2. Metamorphism. When limestone ends up deep in the crust under high pressure and temperature, it becomes marble. According to Geology.com this usually happens where tectonic plates converge and mountain ranges rise, and sometimes next to hot magma.

During the change, calcite recrystallises into interlocking crystals. Recrystallisation is what separates marble from limestone, and it wipes out most fossils and sedimentary layering. The rock never melts: the crystals grow in the solid state. Burial and compaction alone make limestone, not marble; marble needs the heat and pressure of metamorphism. Dolomitic marble forms the same way from dolomitic limestone (James Madison University).

Finnish marbles are 2,100-1,880 million years old (Selonen 2023). The parent rock of Carrara marble was laid down in the Triassic and Early Jurassic, and it became marble when the Alps were folded in the Tertiary (IUGS).

Why does marble have veins and different colours?

Pure limestone gives white marble; colour comes from other minerals. Geology.com explains that clay minerals, iron oxides and bituminous material turn marble bluish, grey, pink, yellow or black, and that pink usually comes from iron. Some well-known examples:

• Bardiglio from Carrara is grey because of abundant, very fine-grained pyrite (Primavori).
• Statuario and Calacatta owe their veins to the micas muscovite and chlorite. Calacatta is also a breccia: pale fragments of marble set in a muscovite- and chlorite-rich matrix (Primavori).
• Lappia Green from Kittilä is green because of fuchsite, a chromium-bearing mica (Selonen 2023).
• Nero Marquina from Spain is black, probably because of dispersed organic matter, and its white veins are later cracks filled with calcite. Geologically it is a limestone (Damas Mollá et al. 2024).

So veins form in two ways: other minerals make bands and layers, or white calcite crystallises later in cracks. Selonen describes marble textures ranging from even-grained to flame-patterned, striped and layered. The finish changes how strong the colours look: the Finnish Natural Stone Association’s materials guide notes that a polished surface shows the strongest colour and a rough one the palest.

This is why every marble piece is unique. Veining and shade vary from slab to slab and within a single slab, and when a piece is made to your own measurements, no two come out the same. A finished marble coffee table will not look exactly like a photo or like another table. The Finnish Natural Stone Association makes the same point: natural stone always carries some variation in colour and appearance. For colours and vein patterns, see our guide to marble types and colours.

How hard is marble?

Marble is soft for a stone: calcite rates 3 on the Mohs scale and dolomite 3.5-4 (Kiviteollisuusliitto). The main minerals of granite are much harder, quartz at 7 and potassium feldspar at 6. With the everyday reference objects in the association’s Mohs table, it works out like this:

In practice, a knife, the bottom of a glass jar and grit carried in on shoes will scratch marble; a fingernail will not. The Natural Stone Institute warns that sand and grit are abrasive and that scouring powders may scratch stone. European EN standards measure stone hardness as Knoop hardness, but the Mohs scale is easier to picture at home (Kiviteollisuusliitto).

Scratches come from hardness, not porosity. Pores affect staining, hardness affects scratching, and calcium carbonate is what reacts with acids. Marble is not hard in the way granite is, but the surface can be restored: a stone restorer interviewed by Use Natural Stone says marble can be refinished an almost endless number of times.

How much does marble weigh?

The weight of a marble slab depends above all on its thickness. Marble’s density is about 2.7 g/cm³, so every millimetre of thickness weighs about 2.7 kg per square metre. Measured densities: Lappia Green from Kittilä 2,640 kg/m³ (Kiviteollisuusliitto, EN 1936), Bianco Carrara 2,714 kg/m³ and the Iranian Pietra Grey 2,770 kg/m³ (suppliers’ technical data).

The weights are calculated at 2.7 g/cm³, and the range at 2.64-2.77 g/cm³. Treat them as a guide: the exact weight depends on the stone, the shape and the edges. A large dining table top easily weighs over 100 kg, so the base has to be sturdy and it takes several people to carry it. That is why we deliver finished tables, table tops and worktops ourselves and install them. For more sizes and weights, see the marble table top page.

Does marble absorb liquids?

Yes, but only a little. Water absorption tells you how much water a stone takes up as a percentage of its weight. Lappia Green absorbs 0.17% (EN 13755), Bianco Carrara 0.1% and Pietra Grey 0.17%. Pietra Grey’s open porosity is 0.47%. That is in the same range as Finnish granites, most of which absorb 0.03-0.3% in the association’s table.

Even that little is enough to stain. In a staining test by the sealer maker FILA to standard UNI EN 16301, oil caused a moderate change on untreated Carrara marble within an hour and a strong change within four hours, and coffee caused a strong change within the first hour. On the sealed surface, neither left any mark even after four hours. The same maker states that its sealer does not protect against acid.

So three different marks can appear on marble, each with its own cause:

How to deal with each one is covered in our guide to cleaning and caring for marble.

How does marble react with acids?

Marble dissolves in acid. Calcium carbonate reacts with an acid to form a salt, water and carbon dioxide. With hydrochloric acid (HCl) the reaction is:

CaCO₃ + 2 HCl → CaCl₂ + H₂O + CO₂

In words: calcium carbonate and hydrochloric acid become calcium chloride, which dissolves in water, plus water and carbon dioxide, which bubbles off as a gas. Material leaves the stone, and a polished surface is left with a dull mark.

Marble and hydrochloric acid in the school experiment

In the classic chemistry lesson, marble chips start fizzing as soon as dilute hydrochloric acid is poured over them. The bubbles are carbon dioxide, and a colourless calcium chloride solution is left behind (Chemguide). Geologists identify the rock the same way: the Finnish geological glossary notes that calcite in particular reacts with dilute hydrochloric acid. Dolomitic marble fizzes only weakly, or only once scraped to a powder (James Madison University), so dolomitic marbles such as Lappia Green and Lappia Ruska fizz only weakly in the test. Do not try it on a finished table: the acid leaves a mark that will not wipe off.

Vinegar, lemon and rain

Kitchen acids etch marble on the same principle. The Natural Stone Institute warns that products containing lemon, vinegar or other acids may dull or etch calcareous stone. Even rain water contains carbonic acid, which slowly dissolves calcium carbonate:

CaCO₃ + CO₂ + H₂O → Ca²⁺ + 2 HCO₃⁻

The same reaction carves caves into limestone (OpenStax), and it explains why marble outdoors loses its polish. It also makes marble useful: crushed marble is used to neutralise acidic lakes and soils, and pure calcium carbonate from marble goes into antacid medicines (Geology.com).

Can marble take heat, frost and the Finnish outdoors?

Indoors, marble copes well with normal temperatures, but it is poorly suited to the Finnish outdoors. The Finnish Natural Stone Association’s materials guide says that, because of its carbonate composition, marble tolerates temperature swings and urban and industrial air badly. It loses its polish, calcitic marbles can etch and weather within a few decades, and some marbles bow. The guide recommends marble mainly for interior surfaces: its suitability table rates polished marble as very suitable for indoor floors, stairs and wall cladding and suitable for kitchen worktops, and does not mark it for any outdoor use.

Always put a trivet under a hot pan. The Natural Stone Institute notes that many stones can withstand heat but still recommends trivets or mats. Stone industry sources give no single temperature limit for marble, so caution is the safe choice. Frost resistance is judged from a stone’s water absorption or a freeze-thaw test (Kiviteollisuusliitto). Lappia Green, for example, is not used outdoors because it contains pyrite that weathers easily.

Finlandia Hall: why did the marble panels bow?

Finlandia Hall is Finland’s best-known example of marble outdoors. In the 1970s its facade was clad in white Carrara marble with blue-grey veins. The marble did not withstand the outdoor conditions and the panels began to bend (City of Helsinki 2020). In 1998-1999 the facade was renewed with smaller panels of Lorano Pradetto marble from the Carrara area, but they too gradually bowed. According to the Finnish Heritage Agency, the original and the renewed facade each lasted only 20-25 years.

A joint study by the City of Helsinki and the EU explained the problem as early as 2001: swings in temperature and moisture damage the structure of marble, and bowing is a sign that its microstructure is loosening. Bowing of a few millimetres showed up on panels only two years old, and durability varied widely even among white Carrara marbles (MTV Uutiset 2001). The city noted that bowing is not just a cosmetic flaw but a sign that the stone is losing strength.

The third facade was chosen by testing. In summer 2018 a test wall with eight materials, five of them different marbles, went up on the roof (Finnish Heritage Agency). In June 2020 the city decided to re-clad the building in Italian Lasa Bianco Nuvolato marble, which did not bow in the tests and was expected to last at least 50 years. According to the producer, about 6,800 m² of marble was supplied in 2022-2023 as 3 cm slabs, and each of roughly 12,000 elements was checked by ultrasound. The choice drew on the EU research project TEAM (2000-2005), and the renovated hall reopened on 4 January 2025.

The lesson for a home: marble for outdoor use is chosen by test results, not by name. Indoors, a table or worktop is not exposed to cycles of frost, rain and sun, so the facade’s problems do not apply in the same way.

Is there marble in Finland?

Yes. Finland has about 650 marble occurrences around the country (Selonen 2023). Most marbles in southern Finland are calcitic, while most in the east and north are dolomitic. The majority have been burned for lime: first for mortar, later for soil improvement and as a raw material for the steel, glass, chemical and cement industries. Almost all southern Finnish marbles are too coarse-grained and fractured to be used as dimension stone.

Finns often call marble kalkkikivi (limestone), even though practically all Finnish “limestones” are marble in geological terms. Unmetamorphosed limestone occurs in only a few places, such as around Lumparn bay in Åland (Selonen 2023) and in small occurrences in Käsivarsi, the north-western arm of Lapland (Tieteen termipankki). Marble was already being mined in Finland in the 13th century, and industrial quarrying began in the late 1800s (Tieteen termipankki).

Finnish stonework began with marble. In 1558 the Dutch stonemason Antonius Timmerman founded Finland’s first stonemasonry business at Näse manor in Perniö, and Vestlax marble was used in the 1556-1563 renovation of Turku Castle. The Loue marble contains stromatolites, which are Finland’s oldest fossils. The Finnish Natural Stone Association calls Lappia Ruska the most widely used marble in Finland, but quarrying of the Lapland dolomitic marbles only continued until the late 2010s, and Lappia Green is now available only in limited amounts (Selonen 2023).

Is everything sold as marble really marble?

No. In the stone trade, any polishable lime-based stone may be called marble (Selonen 2023). In the Finnish Natural Stone Association’s classification, the commercial stone type “marble” covers the geological rocks marble, limestone, dolomite and travertine, and Geology.com notes the name is also used for serpentine. Black Nero Marquina, for example, is geologically a limestone, and green Verde Guatemala is a serpentinite quarried in India. A trade name therefore does not tell you the rock type, and the rock type affects things like how the surface handles acids. Trade names and the rocks behind them are covered in marble types and colours.

Marble-look laminates, quartz composites and porcelain tiles are a different matter altogether: they are not marble at all. We compare them with real stone in marble or quartz.

What do these properties mean for a marble table or worktop?

Marble works well for indoor tables and surfaces as long as you allow for its three weak points: acids etch it, staining liquids can soak in, and harder objects scratch it.

• Coffee and dining tables. The main risk comes from glasses and dishes. The Natural Stone Institute recommends coasters under all glasses, particularly those with alcohol or citrus juice, and trivets or mats under hot dishes. Thickness decides the weight and so the base: a 3 cm slab weighs one and a half times as much as a 2 cm slab. See our marble dining table page.
• Kitchen worktops. A kitchen sees acids, oil and heat every day. The Finnish Natural Stone Association rates polished marble as suitable for kitchen worktops and granite as very suitable. A restorer interviewed by Use Natural Stone notes that etching shows more on polished marble than on honed or textured marble, which makes a honed finish the more practical choice in a kitchen. Read more about marble kitchen worktops.
• Care. Sealing helps against stains, but against acids only coasters, mats and quick wiping help.

The marble we use comes from Iran, which Selonen’s report lists, along with Italy, Turkey, China and India, among the important marble producers. Our Iranian marble page describes the styles of marble that come from there. Once you know where the piece will go, measure the space with our measuring guide and request a quote.