Marble 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 water. Heat and pressure may cause recrystallization. In this way, new rocks are formed, differing widely from the igneous or sedimentary types and usually much harder than either. Thus, shales and related rocks may be altered into slate and limestones into marbles. Marble is, therefore, metamorphic rock resulting from the recrystallization of limestone. Commercially, however, all calcareous rocks produced by nature and capable of taking a polish are called marbles, as are some dolomitic and serpentine rocks. COLOR AND VEINING The color, veinings, clouds, mottlings and shadings in marble are caused by substances included in minor amounts during formation. Iron oxides make the pinks, yellows, browns and reds. Most grays, blue-grays and blacks are of bituminous origin. Greens are caused by micas, chlorites and silicates. TEXTURE The term "texture", as applied to marble, means size, degree of uniformity and arrangement of constituent minerals. Grains of calcite, the chief constituent of most marbles, are crystalline and have definite cleavage which show bright reflecting faces on a broken surface. In most marbles, however, the grains are elongated in one direction by the folding and plication of the beds. SOUNDNESS As a result of knowledge gained in extensive practical experience, marbles have been classified into four groups. The basis of this classification is the characteristics encountered in fabricating and has no reference whatsoever to comparative merit or value. The classifications merely indicate what method of fabrication is considered necessary and acceptable in each instance, as based on standard trade practice. Classification of marble is done by MIA producer and finisher Members. A written warranty should be obtained from them prior to installation. The groupings-A,B,C, and D- should be taken into account when specifying marble, for all marbles are not suitable for all building applications. This is particularly true of the comparatively fragile marbles classified under Groups C and D which may require additional fabrication before or during installation. These four groups are: GROUP A Sound marbles with uniform and favorable working qualities; containing no geological flaws or voids. GROUP B Marbles similar in characterto the preceding group, but with less favorable working qualities; may have natural faults; a limited amount of waxing', sticking2 and filling may be required. GROUP C Marble with some variations in working qualities; geological flaws, voids, veins and lines of separation are common. It is standard practice to repair these variations by one or more of several methods-waxing, sticking, filling or cementing. Liners and other forms of reinforcement are used when necessary. GROUP D Marbles similar to the preceding group, but containing a larger proportion of natural faults, maximum variations in working qualities and requiring more of the same methods of finishing. This group comprises many of the highly colored marbles prized for their decorative values. The Soundness Classifications merely indicate what method and amount of repair and fabrication is necessary prior or during installation, as based on standard trade practices. FINISHES Marble's surface may be finished in a number of ways. In general, smooth finishes tend to emphasize color and veining, whereas rough finishes tend to subdue the veining or markings. Typical finishes are: POLISHED FINISH A glossy surface which brings out the full color and character of the marble. It is not generally recommended for exterior use, or commercial floors. HONED FINISH A satin smooth surface with little or no gloss, recommended for commercial floors. ABRASIVE FINISH A flat non-reflective surface, usually recommended for exterior use. The type of finish desired bears some small relationship to final cost, as the smoother, more highly reflective surfaces require more finishing and consequently more time. The most economical finish for exterior use is the abrasive finish. Other finishes such as axed, bush-hammered, rock-faced, rough sawn, or tooled are also available. THICKNESS Standard thicknesses for marble veneer are generally 3/4 inch (2cm), 7/8 inch (2.5cm), 1 1/4 inches (3cm), 1 1/2 inches (4cm) and 2 inches (5cm).When a marble thinner than 3/4 inch (2cm) is specified, the ratio between thickness and overall size and the use of reinforcing backup materials must be considered. Marble thicker than 2 inches(5cm) is usually regarded as cubic stock. Metric thicknesses given above are approximate; cutting 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. FILLING OF TRAVERTINE Travertine may be obtained from a producer with its normal voids unfilled or filled. Although some finish travertine floors by grinding in place after installation, this practice is less desirable than filling by a finisher in his shop under controlled conditions. Common materials used for filling are natural (gray-colored) or tinted portland cement and clear or colored epoxy or polyester resins. Unless otherwise specified, natural portland cement is used as a filler. Thru-holes and holes larger than a U.S. 25¢ piece in size (25mm) in unfilled travertine should be filled. AGGLOMERATE MARBLE TILES These products are recent introductions to the industry. Typical composition is 90-95% natural marble contained in a cememtitious or resinous binder. Technical details can be obtained from the manufacturer. All references in this manual relate to natural (100% marble), no man-made stone.