The blue crystal is an item use for creating foci. It loads on Old Man Willow. It is worth about 35 gold.

A blue crystal has been left here.
>examine crystal
The crystal is a deep blue and has many facets. It looks to have been cut by an
expert and looks flawless. Upon closer examination, it seems to have an inner
light, pale and only very faintly glowing.

>consider crystal

It is a blue crystal.
It weighs about one pound.