Types of natural stone for interiors: seven families compared

At a glance

Each cell says where it comes from: NSI is the Natural Stone Institute (US trade body) consumer pages; encyclopaedia is a general reference. Properties vary by quarry and bed, so none of this is a specification: the stone workshop's test report for the stone actually supplied is.

Seven stones on one sheet

Marble, limestone, travertine, onyx, granite, quartzite and slate cover most of the natural stone specified for interiors. The drawing sets them side by side. A square mark shows the calcite stones and a round mark the quartz and silicate stones, because that difference explains most of what follows: calcite is soft and dissolves in acids, quartz and feldspar are much harder.

It is a drawing, not a photograph. The colour, veining and grain of a real slab vary from quarry to quarry and bed to bed, so judge any stone from a sample cut from the actual slab. The sheet is a reading aid, not a way to recognise a stone.

What each is made of, and why it matters

Rocks are grouped by how they formed. Granite is igneous: it cooled from magma. Limestone, travertine and the banded calcite sold as onyx are sedimentary, laid down as sediment or by water. Marble is limestone changed by heat and pressure. Quartzite is sandstone changed in the same way, and slate is a mudstone that splits into sheets. The Natural Stone Institute describes quartzite as formed from sandstone and marble as metamorphic; an encyclopaedia entry gives slate as the product of low-grade metamorphism of mudrock.

The minerals matter more than the labels. The Mohs scale ranks mineral hardness from 1 (talc) to 10 (diamond), and its reference minerals include calcite at 3, orthoclase feldspar at 6 and quartz at 7. A steel nail or knife blade is a little over 4 on the same scale (an encyclopaedia table lists ordinary steel at 4 to 4.5). So a steel blade can scratch calcite, and marble, limestone, travertine and onyx are scratchable, where quartz and feldspar are harder than the blade. The scale ranks single minerals, not rocks: a rock is also held together, or not, by its grain size, its cement and its flaws, which is why stone is tested for abrasion, not looked up on the Mohs scale.

The same chemistry decides acid. The Natural Stone Institute warns that marble's calcite ‘is vulnerable to attack by mild acids’, including those found in kitchens and bars, and says the same of limestone and travertine. Our own guide to stone and marble in interiors says a honed face masks etching better than a polish, and natural stone finishes compares the eight finishes.

The properties we could read

Many stone guides print one confident figure per stone for hardness, absorption and strength. We found few that hold across quarries, and a stone sold under one name can come from beds with very different properties. So the table lists only what a source we read gives, with the source, and says ‘no figure’ where we found none. A blank is not a zero. It is a question for the stone workshop's test report.

NSI is the Natural Stone Institute (US) consumer pages; thermal movement is the Tile Association's ‘sample indicative values’ (Table 2, 2013 edition); Mohs figures are for the mineral and come from an encyclopaedia. The table is a reading aid, not a specification.

Two more figures help. The Tile Association (Table 4) lists 25 mm marble at a thermal resistance of 0.05 m²K/W, which is why stone is a good conductor over underfloor heating: see underfloor heating under wood and stone. And one UK limestone producer's manual gives abrasion results of 22 to 26 (BS EN 14157) for its own stone, recommends it for moderate-use floors such as shops, hotels and offices, and cuts it to BS EN 12058 tolerances in sizes up to 600 by 600 mm at 20 mm thick. That is one stone's data, not a figure for limestone in general.

Where each suits, and where to take care

The table sets out what the sources we read say about where each stone suits and where they ask for care. It is not a ranking. The Natural Stone Institute's own principle is that the key is performance: it warns that inappropriate selection leads to unrealistic expectations of a stone, and says the proper research must be completed to be sure the chosen stone will perform in service.

One producer's cautions for its own stone are not a rule for every limestone. Where a source did not cover a use, the cell says nothing. The partner stone workshop confirms what it can supply for each use.

Specifying: name, evidence, weight and the usual mistakes

Names. Trade names do not follow geology. The Natural Stone Institute explains that the stone industry uses nine commercial groups (granite, limestone, marble, onyx, quartzite, sandstone, serpentine, slate, soapstone and travertine), based on how a stone performs, and that a stone's trade name may not match its scientific name. High-density or partly metamorphosed limestones that take a polish are often sold as marble, and most igneous rocks, such as gabbro, are sold as granite. Our own quartzite page adds a caution: some slabs sold as quartzite are in fact dolomitic or part marble and behave more like marble. Ask for the petrographic name, the trade name and the origin together. BS EN 12407 (petrographic description) and BS EN 12440 (denomination) are the European standards for naming; they are named here, not read.

Evidence. Stone Federation Great Britain's checklist for buyers asks for the traditional name, the quarry location and country of origin, the technical characteristics (a CE mark and the product standard, for example BS EN 12058 for floors and stairs), slip resistance relating to the finish being supplied, and the advice on sealing and cleaning. Test methods that give the figures a specification wants are BS EN 14157 (abrasion), BS EN 13755 (water absorption), BS EN 12372 (flexural strength), BS EN 1936 (density) and BS EN 14231 (slip). We name them, and have not read them.

Weight. Multiply the density from the test report by the thickness. The table shows the arithmetic with illustrative densities, not stone data. An encyclopaedia gives granite an average density of 2.65 to 2.75 g/cm³, which at 20 mm is about 53 to 55 kg/m². Our stone page gives typical slab thicknesses of 20 or 30 mm for tops and 12 or 15 mm for wall cladding.

Seven common mistakes (our own list, from the checklist above):

• Naming the stone by trade name alone, with no petrographic name or origin.
• Giving no finish, or no sample to match it (see natural stone finishes).
• Asking for no slip value on a floor, or one that is not for the finish being supplied.
• Leaving out thickness, format and tolerance standard.
• Having no sealing, cleaning or protection clause.
• Approving a small piece in place of the slab, or the range.
• Using a calcite stone in an area that meets acid every day, or a wet area, without checking.

Natural stone: [petrographic name, e.g. limestone] to BS EN 12407; commercial name [ ]; origin [quarry, country]; finish [honed] to match approved sample [ref]; thickness [20] mm; format [600 x 600] mm; tolerances to BS EN 12058 [floors; edition to confirm]. One [bed / block / batch] unless the range is approved.

Test reports for the stone supplied, before fabrication: water absorption (BS EN 13755), density (BS EN 1936), flexural strength (BS EN 12372), abrasion (BS EN 14157) and, for floors, wet slip resistance of the finished face [BS 7976 pendulum / BS EN 14231].

Approved sample [300 x 300 x [20]] mm cut from the production [slab / block], finished and sealed as the works will be, signed, dated and kept on site; range, veining and colour variation agreed before cutting. Sealer [type] compatible with the stone; pH-neutral cleaner only, no acids on calcite stones; floors protected until completion.

Standards and sources

• Natural Stone Institute, consumer pages on stone varieties and on scientific versus commercial definition: read 5 Nov 2026; no page dates shown; US trade body.
• The Tile Association, Tiling to Heated Floors (2013, updated 2014), Tables 2 and 4: read 5 Nov 2026; thermal movement and marble thermal resistance.
• Stone Federation Great Britain, Choosing and Using Natural Stone for your home (2011); a UK limestone producer's flooring manual (not named): read 5 Nov 2026; the buyer's checklist, and one stone's abrasion results and cautions.
• BS EN 12407, 12440, 12058, 12057, 14157, 13755, 12372, 1936, 14231: named, not read; confirm each edition. Encyclopaedia entries: mineral hardness and general geology only.

Questions we are asked

What is the difference between marble and limestone?

Marble is limestone that has been changed by heat and pressure, and both are mainly calcite. In the trade the names overlap: the Natural Stone Institute says high-density or partly metamorphosed limestones that take a polish are often sold as marble because they perform like it. Specify by petrographic name and test result, not the trade name alone.

Is travertine a type of limestone?

Yes. The Natural Stone Institute calls it the land-formed version of limestone, in contrast to the marine limestones. It shares limestone's calcium carbonate base, so mild acids alter it, and it often has natural voids: ask whether they are filled and with what.

Is quartzite harder than granite?

Both are quartz-based and the Natural Stone Institute describes both as hard and durable, with quartzite able to be of exceptional strength, density and hardness. We found no source giving a comparison we could rely on, so ask for abrasion and strength results on the actual stone. Also check the name: some stone sold as quartzite is dolomitic or part marble.

What is onyx, as used in interiors?

The stone sold as onyx for panels and counters is banded calcite from cave deposits, which the Natural Stone Institute calls a sedimentary rock and not a marble. It is translucent and soft. The mineral also called onyx is a banded quartz that is much harder, which is a different material. Ask which one a quote means.

Can natural stone go over underfloor heating?

Generally yes: the Tile Association lists 25 mm marble at a low thermal resistance of 0.05 m²K/W. But stone is rigid, so the floor needs a perimeter strip, movement joints in bays of no more than 40 m² and a flexible adhesive. See our sheet on underfloor heating under wood and stone.

How much does a 20 mm stone slab weigh?

Multiply the density by the thickness. At an illustrative 2,700 kg/m³ a 20 mm slab is 54 kg/m². A source we read gives granite an average density of 2.65 to 2.75 g/cm³, about 53 to 55 kg/m² at 20 mm. Use the density in the stone workshop's test report for the stone supplied.

Why does the stone name matter in a specification?

Because trade names can disagree with the geology and stones in one group behave differently. The Natural Stone Institute says the key is performance and that inappropriate selection leads to unrealistic expectations. Naming the petrographic name, origin, finish and approved sample, with test reports, fixes what you are buying.