San d'Oria Mission 2-3; Can't get Mine Gravel

I am a new player and I am currently stuck on San d'Oria Mission 2-3, Journey Abroad. One of the requirements for the mission is to mine Mine Gravel. I have spent dozens of pickaxes trying to get Mine Gravel, and I have had no luck. I have gone to all the known Mythril Seam locations on the Wiki and the seams keep disappearing after a while when I mine at that spot. I am honestly at my wits end at this point, I need to progress through this mission to get the second Elvaan Trust and yet this one small requirement is barring from doing so. I have tried to bid for it at the Auction House, but I cannot afford it. I have spent days at this, so any tips or tricks to get Mine Gravel would be helpful.

It's a 90% minable item at the seam and the seam never despawns.

It is impossible to find at a "mining point". the Mythril seam on the top floor is something different. It's not that complex.
https://www.bg-wiki.com/images/1/10/...Mines-map3.jpg

I realized my mistake, the Mythril Seams are invisible and I was mining at the wrong spots. Thanks for the help!