Lines like this as well as smooth indents or bubbles do not indicate pontil marks found on handmade marbles.
Marble on microscope.
Check for smooth lines or a single straight line that runs deep into the marble.
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.
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.
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.
They are shear lines caused by machines and are not true pontil marks.
Rocks under the microscope.