LIMESTONE	A sedimentary rock composed of calcium carbonate; includes many varieties (see oolitic limestone, dolomitic limestone, crystalline limestone.) Limestones that contain no more than five per cent magnesium carbonate may be termed calcite limestone, as distinguished from those that contain between five and 40% as the mineral dolomite (dolostone, formerly known as the rock dolomite). Recrystallized limestones and compact, dense, relatively pure microcrystalline varieties that are capable of taking a polish are included in commercial marbles.
GROUP	Sedimentary
COMMON ROCK-FORMING MINERAL GROUP	Calcareous
COMPOSITION	Calcium Carbonate (Calcite) or the double carbonate of Calcium and Magnesium (Dolomite). Contains a variety of accessory minerals... silica, pyrite, iron oxides, clay minerals and bituminous matter from organic materials (plant & animals).
HARDNESS	Soft to Hard. Some varieties are as hard and dense as granite.
MOHS' SCALE	2 - 5
POROSITY	0.6 - 31.0 %
ABSORPTION	0.2 - 12.0 %
WEATHERING CHARACTERISTICS	Depends on the environmental conditions and the type of limestone... Exterior installation in warm humid regions, limestone weathers easily. If iron oxides or pyrite are present, rust spots or runs may appear and if it contains bituminous matter, dark blotchy spots or runs also may appear. Portuguese limestones have been known to contain bituminous matter. Limestone surfaces in any climate may weather irregularly due to the mineral composition of the stone.
TENDENCIES	Absorbs oils and other liquids... Softer varieties have low scratch resistance. Acid sensitive as a rule. However, the Dolomite Limestone varieties are least affected... Some varieties have large pores while others have an open pitted textured surface capable of catching and holding dirt and soil.
COLOURS	Range is in the pastel colours from white to creams through beige to pinkish... soft yellows through browns to rich crimson... medium green to dark blue-green... grey to black. Patterns vary from solid to variegated.
NOTATIONS	Due to the high absorption factor of the majority of limestones it is highly recommended for practical maintenance considerations and to minimize staining, that the stone be treated with a water and/or oil repellent... It is important when choosing the treatment product that the solid content be carefully evaluated or a treatment product that has been specifically formulated for large pored stones be used. Some limestone's surfaces will roughen over time. This is not a form of decay, but merely the surface of the stone developing a natural patina.