For those of you with natural stone floors or considering them
For those of you with natural stone floors or considering them, the following, taken from the article, “The Stone Factory”, by Scott Warrington, is useful information regarding different types of stone floors.
The rock cycle
Stone is a recycled product. Ever so slowly, over long periods of time, stone changes from one type to another.
The rock cycle shows the relationship between different types of stone.
Igneous stone is transported by water, erosion and other natural forces. With time, weathering breaks it down into sedimentary stone. Heat and pressure change sedimentary rock into metamorphic stone.
Movement of the earth’s crust brings metamorphic stone deeper into the earth where it can be heated to the melting point. With further movement of the earth, this heated magma cools to form igneous rock.
Sedimentary stone can be divided into three groupings, according to how the sediment is formed.
Clastic stone begins as rocks that are transported by rivers, glaciers and other forces. It is broken into small particles by ice, rain, flooding and other forces of nature.
Small particles are forced together by pressure.
The biologic type of sedimentary stone is composed of the dead bodies of large numbers of living marine organisms. These settle to the bottom of oceans, pile up and are fused together with pressure and time.
Fossils and shells may be found in biologic material. Because it comes from living organisms, biologic stone will be high in carbon content. It may eventually become coal. Most will form limestone.
The third type of sedimentary stone is known as chemical or precipitate. As water travels through the ground, it dissolves various minerals. When the water evaporates, the material that will form the stone is left behind. Formations in caves are often formed by this process.
Evaporating sea water can also leave deposits that will form sedimentary rock.
Limestone, sandstone and travertine are sedimentary stones commonly used in flooring. Flagstone is often sedimentary. Flagstone is a more general term that can include several types of stone.
The formation of travertine is interesting.
Mildly acidic groundwater dissolves limestone. This is carried deeper into the earth. The mineral-laden water is eventually transported back to the surface, along with water from hot springs.
The water eventually evaporates, leaving the limestone behind. However, gas bubbles have formed voids in the rock similar to Swiss cheese.
When fabricated into flooring, the voids are often filled with a hard resin. The stone expands and contracts with changes in temperature. This loosens the resin. It may come out allowing the voids to be filled with soil. Loosened resin may also come out during the cleaning process.
Metamorphosis is a change from one form to another, like the caterpillar that becomes a butterfly.
Metamorphic stone has been changed from one form into another. The change comes from increased heat and pressure, as well as the introduction of new minerals into the mixture.
The color may change. The texture may change. Under sufficient pressure, the mineral can take on a crystal structure.
Diamond is carbon that has taken on a crystalline structure. Marble is crystallized limestone that has morphed under pressure. The addition of other minerals is responsible for the color. These changes take place deep in the earth under a great deal of heat and pressure, but not enough heat to melt.
To the geologist, marble is always a metamorphic stone composed mainly of calcium carbonate, the same mineral that makes up limestone. However, in the flooring business, any calcium carbonate that takes a high polish may be called marble. This includes some sedimentary limestone.
Another flooring stone that may be referred to as marble is serpentine. Serpentine is actually composed mostly of silicate from volcanic ash, rather than calcium carbonate. A high magnesium content help produce serpentine’s dark green color.
The name serpentine comes from the fact that the texture and markings resemble the skin of a snake. Serpentine is actually an igneous rock. We’ll cover more on that type later.
Slate is another metamorphic material. Like marble, slate is composed of fine crystals. Variations in color result from the presence of additional minerals. The beautiful colors of slate can be brought out by applying an enhancing sealer after cleaning.
Unlike marble, slate is formed from clay, not limestone. This means that slate is not sensitive to acids.
Foliated describes the way slate is divided into thin layers or sheets. These layers give the characteristic appearance of slate.
Formed by molten material deep in the earth known as magma, igneous stones are classified in one of two groupings.
Magma that exits from the surface of the earth, such as in a volcanic eruption, comes in contact with cool ground and much cooler air.
The stone hardens quickly, leaving little time for crystals to form. Igneous rock formed this way has small crystals and is called extrusive.
Intrusive rock is formed when the magma is trapped below the surface of the ground. It cools more slowly and forms larger crystals. Most igneous stone used as flooring material is the intrusive variety.
Granite is the most popular igneous flooring. Granite is crystalline. It has the appearance of grains or veins.
A wide variety of colors are available. Although granite is the hardest stone commonly used in flooring, it can still be porous. It should be sealed to prevent staining.
When minerals are distributed evenly in the granite, there is little or no directionality or appearance of movement. Such stone is called homogenous.
Homogenous granite provides a very durable floor for heavy duty use. Although it will not be very absorbent, it still benefits from a single coat of sealer.
Some granites show a directionality or flow pattern. These are called oriented granite. They are much more absorbent than homogenous granite. Oriented granite is likely to stain permanently if not sealed. Multiple coats of sealer may be required.
A third type of granite is known as veined granite. This shows more distinct veining pattern and a clear directional flow.
Veined granite is the most porous granite. Maintaining multiple coats of impregnating sealer will prevent it from absorbing staining material.