An icicle

Finally figured it out. THe crystals to be cleared are all on the bottom row. Portion of bottom row cleared by star gem in top section (may not be necessary). Then, used two star gems and one flame gem. Placed a star gem at one end of the bottom row. At the other end, placed one star gem and a flame gem. Used star and flame gems to create a blast across the bottom row setting off the second star gem to clear all cells of the bottom row.. Hope this helps. It was a frustrating level and got only one star but it's enough for right now!

Stuck on 650, too.

The green check works.