Really like the idea and the artstyle!!
I found the difficulty extremely hard. Played in easy and couldn't get past level 1-5 after more than 20 tries. :o Most of the times (at least for me), the gems would appear in very bad places, and required to wait and hope for a road to open ahead, being hit or dying in the process, as there's no way to predict where lava is spawning.
Maybe if there where more than one gem or if they changed positions after some seconds, it would help balance the difficulty a little more. :)
I enjoyed the game tho, I believe it has pontential!