Travertine, a natural stone, is a white concretionary form of calcium carbonate that is usually hard and semi crystalline. It is deposited from the water of mineral springs (especially hot springs) or streams holding lime in solution. Extensive deposits exist at Tivoli, Italy, near Rome.

Travertine is sometimes known as travertine limestone, sometimes as traverline marble; these are the same stone even though it is neither limestone nor marble. The stone is characterised by pitted holes and troughs in its surface. While these troughs occur naturally they suggest to some eyes that considerable wear and tear has occurred over many years. Some installers use a grout to fill these holes, while others leave them open. It can be polished to quite a good degree of smoothness and shininess. Many colours are available from grey to a coral red. It is most commonly available in a tile size for interior flooring rather than in flagstone size for exterior paving.


Slate is a fine-grained, homogeneous, sedimentary rock composed of clay or volcanic ash which has been metamorphosed (foliated) in layers (bedded deposits). Slate can be made into roofing slates, or tiles because it has two lines of breakability: cleavage and grain. This makes it possible to split slate into thin sheets.

Slate is mainly composed of quartz and muscovite (a mica), often along with biotite, chlorite, and hematite, or, less frequently, apatite, graphite, kaolin, magnetite, tourmaline, or zircon.

Some of the finest slates in the world come from Portugal, Wales, the east coast of Newfoundland, and the “Slate Valley” of Vermont and New York.


Sandstone is an arenaceous sedimentary rock composed mainly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. Since sandstones often form highly visible cliffs and other rock formations, certain colors of sandstone may be strongly identified with certain regions. For instance, much of the North American West is well-known for its red sandstones.

Sandstones are often relatively soft and easy to work which therefore make them a common building and tiling material.

Rock formations that are primarily sandstone usually allow percolation of water, and are porous enough to store large quantities, making them valuable aquifers. Fine grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices such as limestones or other rocks fractured from seismic activity.

Sandstones are clastic in origin (as opposed to organic, like chalk or coal). They are formed from the cemented grains that may be fragments of a pre-existing rock, or else just mono-minerallic crystals. The cements binding these grains together are typically calcite, clays and silica. Grain sizes in sands are in the range of 0.1mm to 2mm. (Rocks with smaller grainsizes include siltstones and shales and are typically called argillaceous sediments, as are also clays. Rocks with larger grainsizes include both breccias and conglomerates and are termed rudaceous sediments).

The principal mechanism for the formation of sandstone is by the sedimentation of grains out of a fluid, such as a river, lake or sea. The environment of deposition is crucial in determining the characteristics of the resulting sandstone, which on a finer scale include its grain size, sorting, composition and on a larger scale include the rock geometry. Principal environments of deposition may be split between terrestrial and marine.


Porcelain is a type of hard semi-translucent ceramic generally fired at a high temperature.

Porcelain is typically biscuit fired at around 1000 degrees Celsius (1800 degrees Fahrenheit), and glaze fired (the final firing) at 1300°C (2300°F) or higher.

Porcelain clays can be chemically formulated for strength, plasticity and durability to the point that they can be used as throwing bodies. Porcelain ware was produced on the potter’s wheel in many historic cultures, including China and Japan. Many categories of glazes, e.g. celedons, were formulated specifically for their striking effects on porcelain. Modern potters also produce porcelain ware, and generally believe these clay bodies challenge production, firing and glazing skills. Commercially formulated procelain bodies are generally available through most clay distributors.


Marble is a metamorphic rock resulting from regional or at times contact metamorphism of sedimentary carbonate rocks, either limestone or dolostone. This metamorphic process causes a complete recrystallization of the original rock into an interlocking mosaic of calcite and/or dolomite crystals. The temperatures and pressures necessary to form marble usually destroy any fossils and sedimentary textures present in the original rock.

Pure white marble is the result of metamorphism of very pure limestones. The characteristic swirls and veins of many colored marble varieties are usually due to various mineral impurities such as clay, silt, sand, iron oxides, or chert which were originally present as grains or layers in the limestone. Green coloration is often due to serpentine resulting from originally high magnesium limestone or dolostone with silica impurities. These various impurities have been mobilized and recrystallized by the intense pressure and heat of the metamorphism.


Limestone is a sedimentary rock composed of the mineral calcite (calcium carbonate). The primary source of this calcite is most commonly marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze. Secondary calcite may also be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems such as stalagmites and stalactites. A further form is composed of oolites (Oolitic Limestone) and can be recognised by its granular appearance.

Pure limestones are white or almost white. Because of impurities, such as clay, sand, organic remains, iron oxide and other materials, many limestones exhibit different colors, especially on weathered surfaces. Limestone may be crystalline, clastic, granular, or dense, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock. Chert or Flint nodules are common in limestone layers.


The word granite comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a crystalline rock.

Granite is a common and widely-occurring group of intrusive felsic igneous rocks that form at great depths and pressures under continents. Granite consists of orthoclase and plagioclase feldspars, quartz, hornblende, biotite, muscovite and minor accessory minerals such as magnetite, garnet, zircon and apatite. Rarely, a pyroxene is present. Ordinary granite always carries a small amount of plagioclase, but when this is absent the rock is referred to as alkali granite. An increasing proportion of plagioclase feldspar causes granite to pass into granodiorite. A rock consisting of equal proportions of orthoclase and plagioclase plus quartz may be considered a quartz monzonite. A granite containing both muscovite and biotite micas is called a binary granite.

Granite occurs as relatively small, less than 100 km2 stock-like masses and as large batholiths often associated with orogenic mountain ranges and is frequently of great extent. Small dikes of granitic composition called aplites are associated with granite margins. In some locations very coarse-grained pegmatite masses occur with granite. Granite has been intruded into the crust of the Earth during all geologic periods, except perhaps the most recent; much of it is of Precambrian age. Granite is widely distributed throughout the continental crust of the Earth and is the most abundant basement rock that underlies the relatively thin sedimentary rock veneer of the continents.

There are two theories for the origin of granite. The magmatic theory states that granite is derived by the crystal fractionation of magma. Thus granite bodies are the result of intrusion of liquid magma into the existing rocks. The granitization theory states that granite is formed in place by extreme metamorphism. There is evidence to support both theories, and both are useful to explain different observed features. The two may actually merge: as metamorphic conditions increase to the melting point of the metamorphosed granite, it will melt and become a liquid magma, and then harden into igneous granite.

Granite has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. It is also gaining fashion for use as kitchen countertops.


The word ceramic is derived from the Greek word keramikos (the name of a suburb of Athens), and in its strictest sense refers to clay in all its forms. However, modern usage of the term broadens the meaning to include all inorganic non-metallic materials. Up until the 1950s or so, the most important of these were the traditional clays, made into pottery, bricks, tiles and the like, along with cements and glass.

Historically, ceramic products have been hard, porous and brittle. The study of ceramics consists to a large extent of methods to mitigate these problems, and accentuate the strengths of the materials, as well as to offer up unusual uses for these materials.


Pliny used the word basalt and it is said to have had an Ethiopian origin, meaning a black stone.

It is a common gray to black volcanic rock. It is usually fine-grained due to rapid cooling of lava on the Earth’s surface.

The shape, structure and texture of a basalt is dependant on the way it erupted and where it erupted – whether into the sea, in an explosive cinder eruption or as creeping lava flows.

Basalt which erupts under open air forms three distinct types of lava or volcanic deposits: scoria, ash or cinder; breccia and lava flows.

Basalt in the tops of lava flows and cinder cones will often be highly vesiculated, imparting a lightweight “frothy” texture to the rock. Basaltic cinders are often red, coloured by oxidised iron from weathered iron-rich minerals such as pyroxene.

Perhaps the most famous basalt flow in the world is the Giant’s Causeway on the northern coast of Ireland, in which the vertical joints form hexagonal columns and give the impression of having been artificially constructed.