Marble is a metamorphic rock formed when limestone recrystallises under high pressure and temperature. The original limestone fabric disappears and a dense interlocking network of calcite crystals takes its place. That explains its behaviour: marble is dense, takes a mirror polish, and shows the characteristic veining that comes from impurities in the parent rock.
Chemically, marble is almost entirely calcium carbonate. On the Mohs scale calcite sits at 3 — soft, roughly scratchable with a copper coin. Granite, with quartz at 7, is considerably harder.
Trade name versus geology
Be aware that the stone trade calls many materials “marble” that are geologically limestone or travertine. In practice this matters little, because they behave similarly, but in a specification or a conservation report the stone type has to be named precisely.
Properties and limitations
- Acid sensitive. This is by far the most important point. Lemon juice, vinegar, wine, cola, limescale removers and many cleaners attack the surface immediately and leave dull etch marks — straight through a good polish
- Porous and stain prone. Oil, grease and coloured liquids soak in. Impregnating with a purpose made sealer reduces this but does not make the stone immune
- Scratch prone. Grit under shoes acts like sandpaper on a polished floor. A proper barrier matting zone at the entrance is not a luxury
- Outdoors. Polished marble loses its gloss outside and roughens under rain and freeze thaw cycles. For external use choose a honed or brushed finish and a frost resistant variety
Working with it and looking after it
- Finish. Polished, honed, brushed or tooled — the finish governs both appearance and slip resistance. Never specify polished for a bathroom floor
- Adhesive and grout. Always use white, marble suitable adhesive and grout. Ordinary grey cement based products can show through the stone or cause staining
- Cleaning. Only pH neutral cleaners. No scouring agent, no vinegar, no descaler
- Repair. Dull patches and light scratches can be ground out and repolished by a stone specialist; that is a real alternative to replacement
Related terms
- Natural stone
- Metamorphic rock
- Limestone
- Mohs hardness scale
- Stone maintenance
- Terrazzo
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