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Little has been known about the nature of the particles in the fume that accompanies volcanic eruptions of the Hawaiian and Icelandic types, although at times in the earth's history tremendous amounts of such particles must have been emitted into the atmosphere. The fume from I-Ialemaumau crater of Kilauea volcano was sampled in 1965 and 1966 during the absence of an eruption [Cadle et al., 1967; Cadle, 1967; Cadle et al., 1968]. The particles consisted largely of dilute sulfuric acid droplets containing ammonium ions. The 1967 eruption of Halemaumau crater (Figure 1) provided an opportunity to sample and identify particles in the actual eruption fume. Samples were collected from various points about the crater's edge (including the place where Figure 1 was taken) on November 14 and 15 using a Unico multistage impactor operated with a Gelman battery-driven pump. The impactor was modified slightly to permit impaction into both microscope slides, and electron microscope grids mounted on such slides and covered with a film of silicon monoxide.Almost all the particles were collected on the last stage of the impactor, indicating that the diameters were less than about 5/•. Examination of the samples with an optical microscope showed that the particles were largely hygroscopic, water-miscible droplets, plus a few mainly acicular, solid particles. At least two, and possibly more, types of acicular particles were present. Some were water-soluble and optically isotropic, and others were optically anisotropic. Refractive indices of some were measured using a series of immersion liquids of different refractive indices. These particles had a refractive index of about 1.524 and were probably CaSO, ß 2I-I20. Other acicular material was soluble in the Cargille immersion liquids and was probably sulfur. Tests with Nessler's reagent and with an aqueous solution of barium chloride showed the presence of ammonium and sulfate ions, respectively, in the gross collected material.

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