Check for smooth lines or a single straight line that runs deep into the marble.
Marble on microscope.
Some common rock types as seen under the microscope.
Rocks under the microscope.
They are shear lines caused by machines and are not true pontil marks.
Marble width 2 8 cm uk virtual microscope the united kingdom virtual microscope ukvm collection consists of igneous sedimentary and metamorphic rocks from around the uk.
If the marble is completely smooth it was machine made and has no pontil marks.
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.