Understanding Natural Stone: Types, Finishes, and Care Tips

Get to Know Your Stone

Natural stone can be classified into two general categories according to its composition: siliceous stone or calcareous stone. Knowing the difference is critical not only for specifying the most suitable stone for your projects but also for choosing the right cleaning products.

Siliceous stone is composed mainly of silica or quartz-like particles. It tends to be very durable and relatively easy to clean with mild acidic cleaning solutions. Types of siliceous stone include granite, slate, sandstone, and quartzite.

Calcareous stone is composed mainly of calcium carbonate. It is sensitive to acidic cleaning products and frequently requires different cleaning procedures than siliceous stone. Types of calcareous stone include marble, travertine, limestone, and onyx. What may work on siliceous stone may not be suitable for calcareous surfaces.

How to Tell the Difference

A simple acid sensitivity test will determine whether a stone is calcareous or siliceous. You will need about 4 oz. of a 10% solution of muriatic acid and an eyedropper. Alternatively, you can use household vinegar and an eyedropper. Since this test may permanently etch the stone, use a sample, an off-cut, or a corner several inches away from the mortar joint if the stone is already fixed.

Apply a few drops of the acid solution to the stone surface on an area about the size of a 50p coin. If the stone is calcareous, the acid drops will begin to bubble or fizz vigorously. If little or no reaction occurs, the stone can be considered siliceous. Rinse the area thoroughly with clean water and wipe dry. This test may not be effective if surface sealers or liquid polishes have been applied. If an old sealer is present, chip away a small piece of stone and apply the acid solution to the fractured surface.

Caution: Muriatic acid is corrosive and is considered a hazardous substance. Proper head and body protection is necessary when using acid.

The test above is provided for general information rather than for you to attempt yourself. If you are unsure, simply contact us.

Stone Finishes

A polished finish on the stone has a glossy surface that reflects light and emphasizes the color and marking of the material. This type of finish is used on walls, furniture tops, and other items, as well as flooring.

A honed finish is a matte or satin-smooth surface with relatively little light reflection. Generally, a honed finish is preferred for floors, stair treads, thresholds, and situations where heavier pedestrian traffic would wear off a polished finish—not to mention that a honed surface is more slip-resistant. A honed finish may also be used on furniture tops and other surfaces where a matte look-and-feel is desired.

A flamed finish is a rough, textured surface used frequently on granite floor tiles or external paving. Its main benefit is its anti-slip properties.

Stone Colors and Appearance

Granite and marble are quarried worldwide and come in various colors with differing mineral compositions. In most cases, they can be identified by visible particles at the surface of the stone. Marble typically displays "veins" or high mineral concentrations. The minerals in granite will typically appear as small flecks distributed uniformly in the stone. Each type of stone is unique and will vary in color, texture, and marking. That’s the beauty of natural materials.

Sandstone varies widely in color due to different minerals and clays found in the stone. Sandstone can range from light gray to yellow or pink/red. Dark reddish-brown sandstone is also called brownstone, while Bluestone is a dense, hard, fine-grained sandstone of greenish-gray or bluish-gray color and is quarried in the eastern United States.

Limestone is a widely used stone with colors typically in light gray, beige, or buff tones. A distinguishing characteristic of many limestone materials is the presence of fossils that are frequently visible on the stone surface. Typically, limestone is more porous and softer than marble, though there are exceptions.

Slate is usually dark green, black, gray, dark red, or multi-colored. It is most commonly used as a flooring material, especially outdoors, and for roof tiles. Slate is often distinguished by its distinct cleft texture.