marble is a very popular stone for artists to use when carving sculptures. What properties of marble might make it good for sculpting?
Among the commonly available stones only marble has a slight surface translucency that is comparable to that of human skin. It is this translucency that gives a marble sculpture a visual depth beyond its surface and this evokes a certain realism when used for figurative works. Marble also has the advantage that when first quarried it is relatively soft and easy to work, refine, and polish. As the finished marble ages it becomes harder and more durable. Preference to the cheaper and less translucent limestone is based largely on the fineness of marble's grain, which enables the sculptor to render minute detail in a manner not always possible with limestone; it is also more weather resistant.
My initial thought was (2) (one is formed hot, the other not), but a lot of time the shale deposited on top of the basalt, so there would be no contact metamorphism expected (the basalt was already cool). So instead, I would say (3), because both basalt and granite form at high temperatures, and no matter which formed first, the other would be hot relative to the first one that was put into place, and thus would cause a zone of contact (thermal) metamorphism in the earlier rock. 1 and 4 are clearly not the answer.
Marble is chosen because it is softer than metal and it easier to carve than other rocks like a granite or quartzite which are mostly harder than metal tools. Marble is primarily made of metamorphosed calcite and dolomite which both have a hardness on the Moh's hardness scale of 3-4, most metal tools are a 5.5-6. Also, marble reacts with hydrochloric acid so acid can be applied to areas to make them weaker and easier to remove. The term marble is often used when the rock is not really a marble in counter tops or floors. Most marble counter tops and floors have foliation but many marbles are actually not foliated, foliation is a product of regional metamorphism lining up mica minerals perpendicular to the highest level of stress and most limestones (parent rock of marble) don't have micas. Some people actually have gneiss counters and floors. In construction, the term marble is used for an calcitic rock.
