Obsidian deposits in the Cooks Beach-Hahei area (New Zealand) are closely associated with domes of Minden Rhyolite. Small, mainly alluvial and colluvial deposits in the vicinity of dome margins were probably an important source of raw material for the manufacture of obsidian implements in prehistoric time, although little direct evidence of their exploitation remains. Detailed chemical analysis shows that the composition of obsidian within each major source area (Cooks Beach, Hahei) is remarkably uniform. In contrast, there are important chemical differences between source areas, paricularly in titanium, iron, calcium, potassium, and strontium concentrations. Obsidian from Onemana has a similar chemical composition to the Cooks Beach-Hahei deposits but can be distinguished on the basis of calcium, potassium, rubidium, stronium, and Y values. Rb/Sb ratios for each source area are very different. Some problems associated with the sourcing of cultural material Cooks Beach-Hahei obsidian deposits are briefly discussed. -- AATA