Lines like this as well as smooth indents or bubbles do not indicate pontil marks found on handmade marbles.
Marble on microscope.
Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism.
If the marble is completely smooth it was machine made and has no pontil marks.
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.
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.
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.
Rocks under the microscope.