Marble is a 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 dolomite and serpentine rocks. (See "Glossary" for clarification.) 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 are similar in character to the proceeding group, but with less favorable working qualities; may have natural faults; a limited amount of whizzing, sticking and filling may be required.

GROUP C: Marbles with some variations in working qualities: geological flaws, voids, veins and lines of separation are common. It is standard to repair these variations by one or more of several methods杦hizzing, 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 compromises 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.