crystallized exemestane. they may look black but they are not. thats what yellowish crystals in light yellow solution.... look like through a blue filter (UV resistant semi translucent blue PET bottle). it happens.. particularly if solution gets very cold.... (or experienced a large and rapid temperature shift) however even 20-30 particles would be less than 10 mg out of 1250mg solubilized in 60ml...
non issue...
as a side note--- it does have a black cap, and if you consistently severely over tighten.. you could POSSIBLY end with black shavings from cap.. but that would be pretty unusual... VERY unusual.. (as caps are more likely to crack than shave-- it would require improper thread line up AND over tightening..... only reason even mention is do know someone with OCD that has cracked several caps... though he also regularly breaks industrial grade lab ware (overtightening) which actually takes effort or complete disregard for fact thats its closed tight already...