If the marble is completely smooth it was machine made and has no pontil marks.
Marble on microscope.
These are photomicrographs very thin slices of rock seen in plane polarised light or between crossed polarisers when the colours seen are produced by interference of light.
Rocks under the microscope.
Some common rock types as seen under the microscope.
Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism.
They are shear lines caused by machines and are not true pontil marks.
Check for smooth lines or a single straight line that runs deep into the marble.