Natural sapphire or syntetic?

[navneetgems]

Unheated sapphires are much rarer and typically carry higher investment value, while heated sapphires are more budget-friendly and often display brighter, more uniform color.

If you want a deeper breakdown of the differences, you can check out this article:
https://www.navneetgems.com/unheated_sapphires_vs_heated_sapphires/

[LeonidF39263]

Bubbles are generally not typical for natural sapphires. They’re more commonly seen in synthetic, especially flame-fusion material. The RI fits corundum, but the internal features you described point more toward a synthetic stone. A closer look at growth lines or an SG test would help confirm it.