Igneous stone is solidified from molten rock.


Sedimentary stone is created from a blend of organic materials and eroded earth.

Specialization is a growing theme in the tile and stone industry, as products from surface prep to thin sets and even grouts are evolving from a few generic products in the past to premium products available now that are tailored for specific conditions, environments, materials and applications. Thanks to innovative technology, tile contractors now have many options such as lightweight prep, setting and grout products, rapid-setting formulas, job-specific mortars and countless other specialized solutions for just about any scenario to help ensure the success and longevity of a project. Manufacturers of tile and stone installation products are paying close attention to the needs of tile professionals, and developing products to help them solve problems and contribute to the long-term success of projects.

This stunning limestone sink is one example of the many new ways stone is being used to enhance and upgrade interior and exterior spaces.

This trend toward specialization coincides with the spectacular growth of natural stone installations, both in terms of volume and type of installations and also the increased variety of natural stone materials. Amid a still-blazing real estate market, stone is the hottest thing in new home upgrades and remodels, and homeowners are using a wider variety than ever for projects from kitchen and bath upgrades to flooring, patios, barbeques and outdoor kitchens. While granite is still the most popular, accounting for 44 percent of all U.S. stone imports last year, travertine, marble, limestone and slate have caught on big and are showing up in floors, countertops, walls, shower and tub surrounds, pool decks and outdoor hardscapes. This surge in stone use has created a need for specialized care that is just now catching up to demand.

Metamorphic stones evolve when one type of stone changes in form over time, usually the result of extreme heat or pressure.

Understanding Stone Types

In order to care properly for stone installations and preserve their natural beauty, it is important to understand how stone is created. Different types of stone have unique, complex mineral compositions which affect density, porosity, hardness and absorption rates. Stone is categorized in two ways - by its mineral composition, and by its geological formation, both of which affect its properties. All stone used for commercial purposes is eithersiliceousstone, orcalcareousstone. Siliceous stone is made of silica, Earth's most common mineral. Siliceous stone is very hard, very durable, and easy to maintain. Calcareous stone is the second-most-common mineral group, and is softer and more porous that siliceous stone. It is also durable but is sensitive to acids, some of which are found in common household cleaners.

There are three categories of geological stone formations; each is formed above or below the Earth's surface through different processes over millions of years. These categories are igneous stone, sedimentary stone and metamorphic stone.

Acid-based cleaners react chemically with stone, slowly damaging its surface and creating larger pores that can trap stains.

Igneous stoneis solidified molten rock that has been under pressure. Called magma when it is underground and lava when it is above the Earth's surface, this molten rock cools and forms different varieties of igneous rock. Granite is the most commonly used igneous stone. It is a coarse-grained, siliceous-based stone with an even, crystallized texture.

A very hard stone, granite is prized for its high density, low porosity and ease of maintenance. However, granite does have microscopic cracks and fissures between its crystals that make it susceptible to oil- and water-based stains, so proper sealing and cleaning is important.

Electron microscope image of siliceous stone

Sedimentary stoneis created from a blend of minerals and organic plant and skeletal materials that have eroded and broken down through the actions of glaciers, wind, rivers and oceans to form rock beds. Three of the most common types of sedimentary stone are limestone and travertine.

Limestone is derived from seawater and contains minerals and ancient sea creatures. Its texture varies from medium to fine, and generally does not exhibit much graining or crystalline structure. Limestone varies in hardness and is highly porous, making it more susceptible to staining than most other commonly-used stone.

Travertine is a variety of limestone and marble that contains holes formed by pressure, heat and water. These holes are usually filled with resin or other fillers during the fabrication process to create a flat, polished surface, but sometimes travertine is "tumbled" instead to give it a slightly rough old-world appearance.

Electron microscope image of calcareous stone

Metamorphic stoneis created, just as the name implies, from a metamorphism process during which a type of rock formation changes form over time, usually as a result of extreme heat or pressure. The original rock formations may be igneous, sedimentary or another, older metamorphic stone. Typical metamorphic stones are slate, a fine-grained stone formed when sedimentary rock such as shale is changed under high pressure, and marble. Marble was once limestone, compacted by pressure and heat and re-crystallized. They are beautiful but delicate stones, prone to staining and requiring significant care to maintain their appearance.

General purpose sealers contain many various sealing molecules. Some will penetrate and bond but many others will simply be washed or wiped away.

Finishes Make a Difference

The type of finish applied to stone during the fabrication process has a significant effect not only on its final appearance, but also its porosity. Three of the most popular finishes are polished, tumbled and honed.

Polished stone has a very glossy, reflective surface. Its smooth finish brings out the grains and brilliant colors in the stone's crystals, and also reduces porosity. The shine comes from the natural reflection of the stones crystals, and can wear away if subjected to heavy foot traffic and improper maintenance.



General purpose sealers contain many various sealing molecules. Some will penetrate and bond but many others will simply be washed or wiped away.

A tumbled finish has a slightly rough texture, and is achieved by tumbling the stone with small bits of limestone, marble or granite for a worn, old-world appearance. Because the tumbling process does not have the same sealing effect that polishing does, tumbled stone is more porous and more susceptible to staining than its polished counterparts.

Stone with a flat matte or low sheen gloss has a honed finish. Its surface is very smooth, but without the high gloss and vibrant colors characteristic of a polished finished. Honed stone is highly porous and suitable only for low-traffic areas or aesthetics.

Under powerful magnification, it's easy to see the differences in stone types and finishes.

Ideally, a sealer formulated specifically for polished granite will contain penetrating molecules to help the stone "wet out" and allow the sealing molecules to penetrate both the high surface tension and high density of the granite. A formula with the right amount of sealing molecules will create a chemical bond with the stone and provide optimal protection.

Proper Care Maintains Both Beauty and Reputations

After examining these vast differences in types of natural stone and stone finishes, it is clear why specialized care is necessary for optimal results. Each stone reacts differently to the chemical formulas of sealers and cleaners.

Water-based sealers are easy-to-use, non-flammable and contain no toxic fumes. However, solvent-based sealers can be flammable and hazardous - be sure to select a water-based sealer.

General purpose sealers contain various sealing molecules that will penetrate and bond, but some won't and will simply be washed away. An ideal sealer is formulated with the right amounts of molecules to chemically bond with specific stone types and finishes, providing maximum protection.

Common household cleaners should never be used on stone as they often contain acids or harsh solvents that can erode the stone or etch its finish - ruining the stone completely. The acids can also create larger pores in the stone which increases the potential for staining.

Ideally, a sealer formulated specifically for polished granite will contain penetrating molecules to help the stone "wet out" and allow the sealing molecules to penetrate both the high surface tension and high density of the granite. A formula with the right amount of sealing molecules will create a chemical bond with the stone and provide optimal protection.

Today, tile contractors and consumers have more than simply a one-size-fits-all stone care solution. Scientific research and manufacturing knowledge are putting optimized solutions in their hands, from granite cleaners and polishers designed to permeate the dense surface and seal microscopic pockets to protect against stains, to sealers and acid-free cleaners that seal the larger voids in tumbled marble and clean without etching and scratching. These specialized solutions can help protect both the consumer's investment and the contractor's reputation by ensuring the long-term beauty of natural stone installations.