In Wolfram von Eschenbach's version of the grails legend the Holy Grail was (according to translation) called something like "lapsit exillis" or "lapis exillis) - so either a stone that was thrown out of heaven or a rock from the exile, in any case a gem that must have come from very distant and or must have travelled very far.

The concept of the Grail is the mystic bowl that received the fruit of the vine- wine of the Last Supper and the spilled Blood from crucifixion of the Son of god.

3 — obsidian.