Marble is a metamorphic rock caused from the re-crystallization of limestone. Commercially, all calcareous rocks which are created by nature that are capable of taking a polish are called marbles.
The groupings A, B, C, and D should be taken into account when specifying marble, due to the fact that all marbles are not suitable for all building applications. This is true for the comparatively fragile marbles categorized under groups C and D, which may require additional fabrication before or at the time of installation.
These four groups are listed below:
Group A : Sound marbles with uniform and favorable working qualities; containing no geological flaws or voids.
Group B : Marbles similar in character to Group A, but with less favorable working qualities; may have normal faults; a limited amount of washing, sticking, and filling may be necessary.
Group C : Marbles with some variations in working qualities: geological flaws, voids, veins, and lines of separation should be expected. It is standard practice to repair the variations by one or more of several methods: washing, sticking, filling or cementing. Liners and other forms of reinforcement are used when needed.
Group D : Marbles similar to Group C, but containing a larger amount of natural faults, maximum variations in working qualities, and requiring more of the same methods of finishing. This group consists of the highly colored marbles prized for their decorative values.
The soundless classifications merely indicate what method and amount of repair and fabrication is needed before or during installation, based on standard trade practices.
Marble Variations :
Limited Color Variation : relatively uniform in background, veining and/or movement.
Moderate Color Variation : the background color has some variation and some veining; movement may appear. Inspection prior to installation is suggested.
Extreme Color Variation : The background color has significant variations and contrast. Veining variation, as well as, movement may be inconsistent. Inspection prior to installation is strongly suggested.