Longwave should do the trick. Most amber fluoresces with UV, glowing a blueish to green color. Also, amber will float in a heavy salt water. Your piece looks quite a bit like Indonesian amber with the color & fracturing. I would agree! I have 1kg Indonesian amber in my collection because I wanted to see how they are compared to those from other ...
Amber isn't nearly as rare as some may think and many real specimens with insects are found and sold across the world. (More than 1% are genuine). More than 1% are genuine? Are more than 98% inauthentic? This is a sincere question. I would have assumed “1%” was a typo, but my knowledge of amber is too limited to make assumptions.