Crater Lake National Park, Oregon

10. Wizard Island

Examination of the broken lavas on Wizard Island show them to have a dense texture and a nearly black color. Scattered through the black mass may be seen light colored, lath shaped crystals. This type of texture is further evidence that the lavas cooled rather rapidly. A rock which has cooled very slowly is made up completely of crystallized minerals; one which has cooled very quickly is glassy, containing no definitely recognizable minerals. Rocks are colored by their chemical constituents which are directly related to their mineral compositions. Minerals like feldspars, containing sodium, potassium, aluminum, silicon and oxygen, are light colored and where predominant, produce light colored rocks. Where these two extremes are about equal, the rock is intermediate in color and composition. The rocks on Wizard Island and in the walls of Crater Lake belong to such an intermediate group.