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Sunblock mostly absorbs UV (and turns it into heat). Some reflection occurs but it's mostly absorption.

After looking into this even more, there are two types:

Mineral - Reflects

Chemical - Absorbs

I thought so too but it's not the case. Even the mineral sunscreens mostly absorb.

Black means absorbed, of course.

And, omg, you can buy an active version on amazon, for this exact purpose: sunblock coverage check!