The following is an identification guide to several standard types of stone used in sculptures, carving, building construction and similar. The types covered are marble, granite, sandstone, limestone, alabaster and soapstone.
Marble is a high end stone used to make everything from Michelangelo sculptures to mansion steps and walls for mansions. Marble is limestone that was heated longer and transformed in the earth’s crust. It is often mistaken for granite, and visa versa, as the two have the same general look, weight and are used for similar purposes. Luckily, they have several distinct qualities that help tell them apart.
Polished marble is smooth and silky with a highly reflective surface. You can often see your face reflected. If the polished and clean surface has roughness or bumps, it is not marble.
Marble is at least two colors or tones and has a distinct pattern. The pattern grain that runs through it, made up of lines and waves that create a jumbled pattern. Some of the lines may smudge and swirl. If the marble has a speckled or crystal-like markings, then it is more likely to be granite . The colors in marble include pink, black, white, greenish, red and cream. The colors are soft shades, rather than bright.
Marble is very heavy, but relatively soft with a Mohs scale hardness of 3-4. It can be cut by a steel knife. Granite is much harder and cannot. If you cannot cut it with a knife, it is probably granite.
Vinegar will make bubble fizz, whereas granite will be unaffected. The bubbles can be very small so use your magnifying glass to see.
Splash water on the material surface . Marble does not absorb water and water will pool.
If you put an acid liquid like vinegar or lemon juice, marble will react producing fizzing bubbles. The bubbles are very small, so you might need a magnifying glass to se it. Granite does not react.
Granite is a commonly stone used in construction and is often mistaken for marble. Granite is made up of crystal and was heated much as lava is.
Granite is heavy like marble, but much harder. It is 7 on the Mohs hardness scale. Unlike marble, it cannot be scratched by a steel knife. Unlike marble, granite doesn’t react to vinegar, lemon juice or other acids. Granite generally has a more sparkly, granular pattern, as opposed to the fluid lines of marble.
* * * Alabaster
Alabaster is famous as a milky white mineral that can be translucent if carved thin enough.
There are two types of alabaster. One is gypsum, which is used today. The other is calcite, which was used in ancient times including by the Ancient Egyptians.
The two kinds share the same white appearance, but are distinguished from each other due to a difference in hardness. The gypsum kind has a Mohs hardness rating of 1.5-2 and be scratched with a fingernail. The calcite kind has a Mohs rating of 3. It can’t be scratched with a fingernail but can be scratched by a knife
Hydrochloric acid makes the calcite alabaster fizz and bubble, but does not effect gypsum alabaster.
Sandstone is sand turned to rock over time. It formed when grains of sand become cemented together. Sandstone is opaque, with a dull often rough luster. It is usually tan or yellowish, though can be found pink to dark red, and even sometimes blue and green Sandstone is identified by distinct wavy color or tone patterns from how the sand lawyered. Horizontal lines through the stone, indicating the layers, shows it is sandstone not limestone. Limestone is uniform in monochrome (one color).
The hardness varies with sandstone but is often around 7. If you break a part off with a hammer it will crumble with lots of sand. Limestone doesn’t crumble.
* * * Limestone
Limestone is is often mistaken for sandstone, but, unlike sandstone, is one of solid color and much softer (Mohs 3). It can be cut with a knife. Vinegar and hydrochloric acid makes limestone fizzle and pop as it dissolves. Sandstone would be unaffected.
* * * * Soapstone
Soapstone is an attractive stone that has long been used for both practical and decorative purposes. It comes in different colors, including green and pink. When held to the light, soapstone has a smooth, greasy, silky, milky luster. If thin it is transluscent. It is cold to the touch.