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Stone Identification


Natural stone can be classified into two general categories according to its

composition: siliceous stone or calcareous stone. Knowing the difference is

critical when selecting 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, quartzite, brownstone

and bluestone.

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 on

calcareous surfaces.


How to Tell the Difference


A simple acid sensitivity test can be performed to determine whether a stone is

calcareous or siliceous. You will need about 4 oz. of a 10%solution of muriatic

acid and an eye-dropper. Or you can use household vinegar and an eyedropper.

Because this test may permanently etch the stone, select an out of the way area(a

corner or closet) and several inches away from the mortar joint. Apply a few

drops of the acid solution to the stone surface on an area about the size of a

quarter. 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 a small piece of stone away and apply the acid solution to the

fractured surface. CAUTION: Muriatic acid is corrosive and is considered to be a

hazardous substance. Proper head and body protection is necessary when acid is



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 floor tiles.


A honed finish is a satin smooth surface with relatively little light reflection.

Generally, a honed finish is preferred for floors, stair treads, thresholds and other

locations where heavy traffic will wear off the polished finish. A honed finish

may also be used on furniture tops and other surfaces.


A flamed finish is a rough textured surface used frequently on granite floor tiles.



Stone Colors and Appearance


Granites and marbles are quarried throughout the world in a variety of colors with

varying mineral compositions. In most cases, marbles and granites can be

identified by visible particles at the surface of the stone. Marble will normally

show "veins" or high 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.


Sandstones vary widely in color due to different minerals and clays found in the

stone. Sandstone is light gray to yellow or red. A dark reddish brown sandstone,

also called brownstone, has commonly been used in the northeastern United

States and eastern Canada.


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 building stone with colors typically light gray, tan or

buff. A distinguishing characteristic of many limestones is the presence of fossils

that are frequently visible in the stone surface.


Slate is dark green, black, gray,

dark red or multi-colored. It is most commonly used as a flooring material and for

roof tiles and is often distinguished by its distinct cleft texture.