Gemmology: If the round/oval droplet appears half light and dark, with a line across the middle when using the distant vision technique, what does this mean?

Question

If the round/oval droplet appears half light and dark, with a line across the middle when using the distant vision technique, what does this mean?

Emma Begent-Cove · Accepted Answer

RI of stone is at centre of droplet

If the round/oval droplet appears half light and dark, with a line across the middle when using the distant vision technique, what does this mean?