Derived from limestone or dolomite, marble is a metamorphic rock created by pressure and heat within the earth's crust. In its pure state marble is white, but due to mineral impurities it can be found in a range of colors – preponderantly yellow, brown, green, pink or black – and with various speckled and veined effects. Prized for its decorative appeal, it has been used for centuries as a building material and medium for sculpture. The main problem with identifying marble arises from its similarity in some respects to granite, onyx, alabaster and even porcelain, but with a few tips should help you to tell the difference.
Lift the item – assuming it is a freestanding item – to see how heavy it is. Marble is a very heavy, dense material, so even relatively small items will be noticeably heavy. For this reason, it is often used to make decorative paperweights and bases for bronze figurines. One good way of telling the difference between marble and onyx – which is also used for decorative bases – is that a piece of marble will be heavier than a similarly sized piece of onyx.
Scratch the underside of the item with a penknife. On marble, the blade should leave little or no mark. If the blade sinks in, you are handling some other kind of substance – for example, alabaster, a soft pale stone which is sometimes confused with white marble.
Turn the item under a source of light and examine its sheen. On polished marble this is distinctively waxy and luminous in a way that has been compared to human skin. This is because the light penetrates into the stone a little bit before being reflected back. The sheen on polished onyx and granite is harder and more glossy.
Look to see how the item has been made, in the case of figurines. Pieces made out of bisque – that is, unglazed porcelain -- can sometimes be confused with pure white marble, but you can easily tell the difference by examining the base. A marble piece will have been carved from the solid, and the base will therefore be flat. A piece of bisque porcelain will have been cast rather than carved, so it will be hollow. You should be able to tell this from the presence of a hole in the base for the release of hot air during the firing process.