Cut Pearl into Two Halves - Cultured or Synthetic Pearls?

Dear Sir, please be informed the jewelers where i live are either uneducated or unknowledged in pearls and that is why i am asking your opinion.

I can give you more information i.e. i burned one small bead of pearl with jeweler torch and the pearl cut into 2 half pieces through normal magnifier , i barely see contour lines on cut surfaces and since heat burned and removed external layers of pearl , on some points of exterior surface i can see different colors and i am not sure whether it is pearl shining "rainbow" or artificial colors . i hope am information will be helpful to guess whether the pearl is cultured or artificial & its value.
with regards
Ali