Figure 17. Blue Dragon

The mineralization within Crystal Pit spatter cone is unique. This open chamber contains large quantities of the secondary sulfate minerals, gypsum, mirabilite, and jarosite, all of which seem to be scarce or absent in caves in other volcanic regions. Crystal Pit is a teardrop shaped cavity approximately 120 feet (36m) deep that most likely fed the spatter cone at the surface. Microcrystalline mirabilite (Na₂SO₄•10H₂O) and crystalline gypsum (CaSO₄•2H₂O) are abundant at the bottom of the pit, covering the walls and jarosite ((KFe₃(SO₄)₂(OH)₆)) occurs as a loose powdery yellow material on the cave floor (Peck, 1974). The presence of such large quantities of these minerals in a volcanic cave is at best unusual and their origin is still unknown. Peck (1974) proposed that the mirabilite and gypsum are likely capillary groundwater deposits. Another suggestion is that the minerals are precipitates from an underground lake in Crystal Pit. However, the rocks forming the bottom of the pit are porous and would not likely allow a lake to form. Thus, the origin of these minerals is still in debate.

A unique blue lava surface is found on a few flows in COM lava field. One flow has been named the Blue Dragon lava flow because of the color (Fig. 17). This pahoehoe lava flow extends southwest from the base of Big Craters and was first noted by Russell (1902). The broken lava surface seems to have a series of color layers to the naked eye. The outermost layer is a thin (<5µm) film that appears pale to deep blue. Beneath this layer is a 0.1 inch (3mm) thick blue colored glass layer that grades with depth into a brown glass. Thin sections of the flow surface appear brown in transmitted light but the outer blue glass appears blue in reflected light. Faye and Miller (1973) suggested that the blue color is as a result of an electron transfer between iron ions or iron and titanium ions due to oxidation that alters the light absorption in the rock surface. The reason for this blue color is not yet clearly understood, and awaits further research.