Most likely either lab grown corundum (sapphire) or lab grown spinel. Both very popular in large size cocktail style rings.
You can’t use any sort of gem tester to seperate lab grown from natural.
You need to look for, with magnification, inclusions that indicate natural origin. Perfectly clean appearing stones are typically lab grown. Nature is rarely perfect.
Lab grown also have a growth pattern called curved striae, which you can see with magnification if you know what to look for.
Nothing wrong with lab grown gemstones, they can be just as beautiful as natural however they are worth very little being mass produced.
yes, I agree with this.The little specks you are seeing are likely gas bubbles. A real sapphire would be set in a higher quality setting (diamonds, straight prongs, etc). This is pretty certainly a synthetic.