No problem - I had actually seen this thread earlier but didn't find a satisfactory answer in it. I will try the very very slow crystallization as suggested by AWK, but are there any other tips you can give me?
Maybe it'll help if I am more specific about what I did: So I crystallized out of water. I brought 100 mL of water to a boil and made a saturated solution of the boric acid. I poured that boiling water into another beaker and let it cool to room temperature, which took about a half hour or so. I then put it in the fridge for 10 minutes, followed by an ice bath for 15 minutes. I filtered out the crystals. The crystals that were floating on top of the solution were flat and flake-like. They were also pearlescent, just like the ones in the picture above - though they were quite small . The crystals that settled on the bottom and that were stuck to the side were more granular, like salt.
So what I did partially worked. Based on what I just described, any more advice?