Limestone GEOLOGICAL CLASSIFICATION Rocks may become plastic under great pressure and high temperature and by earth movement. They may be folded into complex forms with a banded structure. Many constituent minerals may be dissolved, transported and reprecipitated by thermal waters. Heat and pressure may cause recrystallization. Limestone is defined as a rock of sedimentary origin composed principally of calcium carbonate orthe double carbonate of calcium and magnesium or a combination of these two minerals. Recrystallized limestones, compact microcrystalline limestone and travertines that are capable of taking a polish are promoted, marketed and sold as either lime- stone or marble, particularly in the United States. Dimension limestone is divided into three subclassifi- cations that describe their densities in approximate ranges, as follows: Low Density - Limestone having a density ranging from 100 through 135 Ib/ft3 through 2160 kg/m3) Medium Density - Limestone having a density greater than 135 and not greater than 160 Ib/ft3 (2160 through 2560 kg/m3) High Density - Limestone having a density greater than 160 Ib/ft3 (2560 kg/m3). COLOR AND VEINING The color, veinings, clouds, mottlings and shadings in limestone are caused by substances included in minor amounts during formation. These include iron-bearing minerals, clay and organic material thought to be residual from the soft parts of tiny marine animals. Most of these dark materials are found between calcite crystals or the shell materials and some shells and calcite crystals are darker than others. Iron oxides make the pinks, yellows, browns and reds. Most grays, blue-grays and blacks are of bituminous origin. TEXTURE The term "texture", as applied to limestone, means size, degree of uniformity and arrangement of constituent minerals. Limestone contains a number of distinguishable natu- ral characteristics, including calcite streaks or spots, fossils or shell formations, pit holes, reedy formations, open texture streaks, honeycomb formations, iron spots, travertine-like formations and grain formation changes One or a combination of these characteristics will af- fect the texture. FINISHES Limestone surfaces may be finished in a number ol ways. Typical finishes are: POLISHED FINISH A glossy surface which brings out the full color and char- acter of the limestone. HONED FINISH A satin smooth surface with little or no gloss. SMOOTH FINISH Smooth finish, with minimum of surface interruption. PLUCKED FINISH A rough texture. ABRASIVE FINISH A flat non-reflective surface. SAWN FINISH A comparatively rough surface; can be chat, shot, sand or diamond sawn. Other finishes such as machine-tooled or thermal are available. Some stone finishes can affect strength and durability. Examples are bush-hammered and thermal finishes which initially reduce a stone's thickness and also make it more vulnerable to weakening from exposure to freeze and thaw cycles. The type of finish desired bears some small relation- ship to final cost, as the smoother more reflective sur- faces require more finishing and consequently more time. THICKNESS Standard thicknesses for limestone are generally 3/4 inch (2cm), 1 1/4 inches (3cm), 1 1/2 inches (4cm), 2 1; 2 inches (6.4cm), 3 inches (7.6cm), and 3 1/2 inches (9cm) and 4 inches (10cm). Metric thicknesses given above are approximate; cut- ting can be made to exact metric measurements through conversion of English values to metric equivalents. Note that as granite is cut thinner its tensile strength is diminished.