14 x 18 mm Oval Black and Green Agate Slice Glass Magnetic Clip Non Pierced or Pierced Earrings
These look like geode slices in green and black but they are made of glass.:
They are 14 x 18 x 6 mm high.
The magnetic style is held on the ear with one nickel plated 5 mm neodymium magnet attached to the earring and one 8 x 3 enamel painted ceramic magnets that goes behind your ear to hold it on.
Need extra or stronger magnet backs? They are listed here:
Remember: The wider the magnets, the more comfortable the earring is.
If you have misplaced your metric ruler, remember that 13 mm=1/2 inch.
If you are allergic to nickel, order only earrings that have both enamel painted ceramic magnets front and back since the neodymium magnets are plated with nickel.