Here is the full list of all 14 Just Bones achievements.
Complete cave section
Find twenty keys
Die in lava for the first time
Find ten keys
Complete all tutorial levels
Find your first key
Get three stars for the first time
Fall into pieces for the first time
Complete ten levels with three stars
Complete twenty levels with three stars
Jump into swamp for the first time
Complete mountain section
Complete swamp section
Complete thirty levels with three stars