Looks the same as an icicle, but it does not melt. It also makes somehow good decoration item.
10 of these are needed to do Shadows of Yalahar Quest. They can be obtained by picking a slain earth elemental during the 3rd mission. After giving crystals to Telas it is no longer possible to gather them.
Buying them directly from Black Bert is somehow useless as crystals are relatively easy to get, much easier than leather with obsidian knife.</spoiler>