The Carving Stone Company
This is the introductory page to a section that has been created to explain some of the diverse and sometimes confusing terminology used regarding carving stone. The list of terminology that we have created is drawn from various areas, but all of it is meant to be relevant to the stone sculptor.To find out more information about how a mineral is different from a rock and the properties of minerals that are important for sculpture visit our Mineral Properties page. To find out information about characteristics that are important to stone carving visit our Stone Characteristics page (currently under construction). These pages have been created from our desire to help you have a better understanding of stone and because of your requests for information. If you have any suggestions regarding information you would like to see included in these pages let us know.
The following information will hopefully help clarify some of the terminology that is used on our website, amongst stone sculptors, and in the commercial stone industry, the latter of which is especially known for using many different terms without consistency. This list uses red for generic terms that are used commonly by industry, and blue for more precise mineral names. Mineral names are followed by the chemical composition (except those that are more complex) and the symbol "H" with a number indicating the hardness. This information is not meant to be comprehensive as there are many more (possibly hundreds) of stones that can be carved so we have tried to cover the most commonly carved stones, and some of the more unique carving stones that we may have in stock.
Alabaster - Usually describes the mineral Gypsum, especially the varieties that are compact, take a good polish, and often have some degree of translucency. This term has occasionally been applied to some types of very pure, fine grained and semi-translucent Marbles such as much of the stone used in ancient Egypt for both functional and decorative objects.
Anhydrite - (Calcium Sulfate - H 3.0 - 3.5) Similar composition as Gypsum less chemically combined water molecules giving the stone its name which means "without water". Anhydrite can be formed by the loss of the water molecule from Gypsum, or vice versa - Gypsum can be formed by the hydration of Anhydrite. A rare variety of Anhydrite of light blue color is known as "Angelite". Although it has a hardness greater than Alabaster, Anhydrite often has some of the same desirable sculptural qualities such as a beautiful color and a high level of translucency, in addition to taking an excellent natural polish.
Argillite - A non-fissile (no layering) variety of shale or slate. A sedimentary rock formed predominantly from a mixture of clay and other minerals. Its extremely fine grain is known to take excellent detail in carving. Most commonly having a grey to black coloring, but many other colors are known. See Pipestone.
Brucite - (Magnesium Hydroxide - H 2.0 - 2.5) Sometimes occurs with and is sometimes confused with Soapstone because of its appearance and softness. Commonly found in association with dolomite, which will increase the hardness of the stone. Has an appearance most commonly ranging through white, yellow, lime green to dark green and grey. Is mined commercially because of its high magnesium content, but is a somewhat rare mineral.
Calcite - (Calcium Carbonate - H 3.0) Calcite is one of the most common minerals on the earth and makes up or is strongly related to a large part of the stones that are used for sculpture, namely marble and limestone, dolomite, travertine in addition to others. Pure Calcite is used as the indicator for 3.0 on the hardness scale.
Chlorite - (H 2.0 - 3.0) This term is often used to distinguish a group of similar minerals, but is often treated as one mineral. Most often in shades of green to black, but can be found in other colors. Due to its common occurrence with Talc and its relative softness is sometimes classified as soapstone.
Dolomite - (Calcium Magnesium Carbonate - H 3.5 -4.0) Similar composition to limestone but with higher magnesium content. Often called "Dolomitic Limestone", "Magnesium Limestone" or "Dolostone". Often cannot be distinguished from Limestone/Marble without further field or laboratory testing. This stone is a little bit harder and is more resistant to weathering (or acids) than a true Limestone/Marble.
Fuchsite - One variety of a class of mica which is known as Muscovite. Fuchsite is also known as Mariposite. Green to Bright emerald green in color.
Granite - Used to identify a group of minerals that often contains Quartz, Feldspar, Plagioclase, etc and are igneous (or seem to be) in origin. In the building stone market, has been expanded to include some stones that have "Granite - like" qualities. Stones classified as Granites are generally quite hard.
Gypsum - (Hydrated Calcium Sulfate - H 2.0 - 2.5) Most commonly formed from precipitation of sea water or alteration of Anhydrite. Pure gypsum is used as the indicator for 2.0 on the hardness scale. An important industrial mineral used for the manufacture of plaster and wallboard.
Jade - This term has been applied to two different minerals similar in appearance, both being relatively hard, and tougher than steel. The first is Jadeite (H 6.5 -7.0) more commonly known as the stone traditionally carved in Asia and central America and is considered by some to be more valuable of the two varieties. The other variety is a variety of the mineral Actinolite (Nephrite, H 5.0 - 6.0). Both of these stones are most commonly recognized in the green variety, but also can be found in white., black and brown as well as other colors.
Limestone - (Calcium Carbonate) Limestone by definition contains at least 50% calcium carbonate by weight. A sedimentary rock formed by a chemical transformation in relation to various organisms such as coral, algae, and bivalves. Also formed as a carbonate precipitate around small particles in water (eg. Indiana Oolitic Limestone), or is deposited by waters rich in calcium carbonate (Travertine). Fossils are often visible in Limestone.
Magnesite - (Magnesium Carbonate - H 3.5 - 4.5) Another carbonate having "Marble-like" qualities and appearance.
Marble - Applied to a range of carbonate based rocks, most often to describe a recrystalized limestone, or a non-crystalline Limestone, Magnesite or Dolomite which is able to take a good polish. This term is often one of the most widely used in the commercial stone trade and has also been (mis-)applied to a wide range of different non-carbonate types of rocks that have some kind of "Marble like" texture or patterning and can take a good polish. One of the most common examples of this is a type of green Serpentine that often has white veining, which is labeled Verde Antique Marble.
Onyx - This word was originally used only to describe a black and white banded Chalcedony (Quartz), specifically one with wide and flat bands. However in commercial terminology this term has been adapted for many types of semi-translucent to translucent banded varieties of many different stones. This includes other types of Quartz as well as Calcite, Marble and Travertine (often called Onyx Marble) and even some Alabasters. The so-called "Mexican Onyx" is a very common example of a multicolored and banded Calcite.
Pyrophyllite - (Hydrous Aluminum Silicate - H 1.0-2.0) This mineral is very similar to talc in chemical makeup and in appearance and there is sometimes difficulty in distinguishing between the two minerals without analysis. Pyrophyllite has similar industrial uses to talc, although its occurrence is not as widespread. Much of the pyrophyllite used for carving purposes has a hardness greater than soapstone, somewhere between the hardness of alabaster and marble. One of the most commonly carved types of pyrophyllite is a variety from Africa known as African Wonderstone.
Pipestone - Denotes a term that carvers have used for the mineral Argillite generally of the reddish brown variety which is also known as Catlinite.
Serpentine - Relatively common, usually classified as a group of related minerals in the Hydrous Magnesium Iron Silicate family (similar to Talc and Chlorite) and can have a hardness ranging from 2.5 to 4.0. Usually colored green with shades of white, yellow and black. Is commonly sold as polished slabs and tile under the name Verde Antique Marble.
Soapstone - Most commonly used to describe a stone that is predominately composed of talc, from which its slippery feel it got its name. As a generic term has sometimes been used to include stones that are often geologically related to talc (eg. Chlorite, Serpentine) and occasionally is applied to stones that are not related to talc at all. Another stone that is sometimes grouped in this classification is the mineral pyrophyllite (also known as Wonderstone), which has similar chemical composition and appearance, and is usually slightly harder than Talc.
Steatite - This term was traditionally used to describe massive talc of high purity, generally interchangeable with the term Soapstone although may imply a slightly greater hardness than is associated with the term soapstone. This greater hardness of Steatite may be due to other minerals in the stone other than talc, or a crystal structure that is finer or denser.
Talc - (Hydrous Magnesium Silicate - H 1.0) Pure Talc is used as the indicator for 1.0 (the softest mineral) on the hardness scale. Talc is an important material for many industrial applications because of its resistance to heat electricity and acid and is used in many applications as a filler or as a whitener. Two of the most common occurrences of talc are "Ultramafic" (meaning ultra-dark) and "Carbonate hosted". Ultramafic talcs usually come in darker shades of brown, green and black. Other carving stones associated with this type of deposit are Chlorite and Serpentine. Carbonate hosted talcs are associated with Dolomitic marbles and generally come in lighter shades of white, pink and green.
Travertine - A Limestone deposit formed by the evaporation of spring water rich in calcium carbonate. Tends to be porous and often has banding or layering from various impurities.
Wonderstone - This is a term commonly used to describe the stone Pyrophyllite. Most well known is a dark grey to black variety found in Africa, although there are additional occurrences in many countries throughout the world in a variety of colors.
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