Metamorphic stone has been changed over time by pressure and heat of geological force. Perhaps the most-used metamorphic stone is marble. It comes in many colors, including white, black, red, pink and green. Marble is hard enough to be strong and hold its shape for thousands of years, but soft enough for artists to carve with intricate details. Other metamorphic rocks include serpentine, which is green to greenish-black, and is about the same hardness as marble, allowing it to be carved and then polished. Another metamorphic rock is slate, which comes from shale and is usually a dark color.
Sedimentary rock is created in layers over time. Because of they way they are formed, sedimentary stones often have fossils trapped inside. Limestone is the sedimentary rock most often used for carving. It is created when calcium carbonate forms on the bottom of a lake or sea. It is a 2 1/2 on the hardness scale, making it quite soft, but hard enough to polish. Other sedimentary rocks used in carving include travertine, which forms in the bottom of hot spring pools, and sandstone, which consists of millions of grains of sand that cement together over time.
Igneous rock is stone that used to be molten and then cooled near Earth's crust. Igneous rock is among the hardest rock that can be carved, which also makes it the most durable and sustainable. Granite is probably the best-known igneous rock and the one commonly used for carving. Granite, which rates a 6 1/2 or 7 on the hardness scale, is chiefly composed of the minerals quartz, mica and feldspar. Other igneous stones include diorite, diobase and basalt. These stones, like granite, are usually black, but are sometimes dark brown or green.
Soapstone does not fall under the classification of the other types of stone, as it contains traces of many different stones. Among them is talc, which is a 1 on the hardness scale and can be carved with the pressure of a fingernail. Soapstone varies in color, from blue and green to black, and the darker colors of soapstone tend to be harder. Alabaster has the white-lined beauty of marble, but is much softer and easier for beginners to carve. It is made primarily of gypsum and is also crushed up for artists to use as plaster.