They are shear lines caused by machines and are not true pontil marks.
Marble on microscope.
Lines like this as well as smooth indents or bubbles do not indicate pontil marks found on handmade marbles.
Check for smooth lines or a single straight line that runs deep into the marble.
Rocks under the microscope.
Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism.
It is composed primarily of the mineral calcite caco3 and usually contains other minerals such as clay minerals micas quartz pyrite iron oxides and graphite.
If the marble is completely smooth it was machine made and has no pontil marks.