Pure Ironbark is a plot item in Dragon Age II used with the quest Herbalist's Tasks during Act 1.
Ask Master Ilen in the Dalish camp in Sundermount for directions. Upon asking him, a new location on the map appears: Ironwood Clearing. Go there to collect the item.
Note: This is a new world map location, not a location within Sundermount.
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Somewhat blue in color, this rare wood is found only in the Brecilian Forest. It is surprisingly strong and is very light.