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 works on siliceous stone may not be suitable on calcareous surfaces.

How to Tell the Difference

A simple acid sensitivity test can be performed (wear the appropriate safety garments) to determine whether a stone is calcareous or siliceous by using household vinegar and an eyedropper. 

Because this test may permanently etch the stone, select an out of the way area (a corner or cupboard) and several inches away from the mortar joint.  Apply a few drops of the vinegar to the stone on the area about the size of a 5p coin.  If the stone is calcareous, the acid drops will begin to bubble and 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. 

Stone Finishes

A polished finish on the stone has a glossy surface that reflects light and emphasizes the colour 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.

A flamed finish is rough and develops through intense heat. During fabrication, the stone is heated and the crystals expand open and melt to form the roughness. This surface is very porous and must be treated with either Stain-Gard Impregnator or a Nu-Life seal depending on your required finish. 

A Sand Blasted surface results from effect of the surface being

bombarded by sharp particles under pressure in a water/sand mix.  This results in a finish which is described as matt gloss.

A bush-hammered surface results from a pounding action that develops a textured surface. It can be done using pneumatic tools although there are specially made heads designed for single disc floor machines.  The degree of roughness can be varied on most stones to give a fine, medium or rough appearance.

A tumbled surface has a slightly rough texture that results from tumbling pieces of marble, limestone and granite to achieve an archaic or worn appearance. Usually this is reserved for small tiles more often than not used on wall surfaces.  This surface often requires application of a Nu-Life stone enhancer to bring out the colours.

Stone Colours & Appearance

Granites and marbles are quarried throughout the world in a variety of colours 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 colour, texture and marking.

Sandstones vary widely in colour due to different minerals and clays found in the stone.  Sandstone is light grey to yellow or red.  There is also A dark reddish brown sandstone called brownstone. 

Bluestone is a dense, hard, fine grained sandstone of greenish-grey or bluish-grey colour. 

Limestone is a widely used building stone with colour typically light grey, tan or buff.  A distinguishing characteristic of many limestone’s is the presence of fossils that are frequently visible in the surface of the stone.

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