Marble forms from limestone under high heat and pressure, typically in mountainous areas or near tectonic plate boundaries. An 'X' would be placed on the cross-section in areas representative of these conditions. It's characterized by its recrystallized carbonate minerals and unique colorations.
The metamorphic rock marble will most likely form at a location with significant heat and pressure conditions.
Marble is metamorphosed from limestone, which requires exposure to these conditions to recrystallize into a harder and denser form.
To identify a location for the formation of marble, one would look for areas with geological features that suggest intense heat and pressure, such as near tectonic plate boundaries or in regions with a history of volcanic activity.
Mountains and subduction zones are exemplary locations where such conditions are met.
Given that marble is typically found hundreds of feet deep across a mountain, any cross-section indicating the presence of a mountainous region would be a probable candidate for placing an X to indicate where marble could be formed.
The recrystallization process involves both dolomite or calcite and occurs under subsolidius conditions—temperatures high enough to alter the rock's structure but too low to cause melting. Impurities in the limestone lead to the unique colorful patterns found in the marble.