Iron Deficiency is a optional Task you can complete in Alabaster Dawn, available once you begin the Journey Up North story in Chapter One.
To start this task, you need to speak to Petros in Lyhamn Center.

Petros is in need of Iron to help crafting items and Juno thinks her Dad knows where to find some.
Head to Lyhamn - Memory Garden and speak to Solon, your dad.
Solon believes you can get some Iron from sand, and heads back to Petros to explain. Solon tells you to meet him at Median Divide to look for the source of sand.
Meet Solon at Median Divide

Median Divide can be found east of Kamu Village.

When you reach the river edge, Solon appears.

After taking out some Nuemera, you can then use your Divine Vision to locate the sand in the river bed.
You're then tasked with finding four more samples of Iron Sand. You can use your Divine Vision to locate them.

Three of them can be found in the river bed near where Solon is.

The fourth one can be found in a small cave in the same river; approaching it causes Nuemera to rush out.
Speak to Solon once you have all the sand. You'll then have to fight off some more Nuemera.
Find grandfather o' Lira's hidden Vault

The final part of the task is to find the hidden vault. It is located just north of the Median Divide.

To reach it, you need to climb up onto the cliff nearby, and then jump to the right to make your way past the waterfall.

From there you can make a jump across to the main cliff and jump onto the Nyx Rot to lower the barrier.

Enter the cave to complete the task (there's nothing in there anyways!).
Head back to Petros to turn in the task.

Reward: Simple Knife.
You can then turn in the Simple Knife as the Wellspring for Ruff Edge Blueprint and Whisper of the Gods x4.
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