06 Chemical Composition

Pumice Deposits of the Klamath Indian Reservation, Klamath County, Oregon

Chemically the pumice of both the flow and the fall deposits is similar over the entire area and is of dacitic composition. The principal chemical constituents are silica, alumina, and soda. On the basis of chemical analyses listed in Moore (1937) and Williams (1942) a typical pumice sample contains about 69 percent SiOZ, about 15 percent A12 03 , slightly more than 2 percent combined Fe 2O3 and FeO, about 2 percent CaO, less than 1 percent MnO and MgO, about 5 percent Na2 O, a little over 2 percent K2 0, and very small amounts of TiO 2, P2 05 , plus approximately 3 percent H2 0. A quick determination of the chemical character of the pumice may be made by determining its index of refraction, and the indices of many samples from different parts of the Reservation were determined. The range of index of refraction in the samples tested was from 1. 500 to 1. 518. This indicates they are all of about the same dacitic composition.

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