<p> Altered olivine tholeiite basalt on Mauna Ulu Volcano, Hawaii was examined petrographically and chemically to determine the mineralogy of the alteration products. Colour plays an important role in determining a general trend of alteration. </p> <p> The processes involved in the formation of Mauna Ulu have little effect on the alteration. The major influence is the type of volcanic gas and its constant interaction with the basaltic lava over an eight year period. The gas is oxidized as it cools, resulting in a zoning of different alteration products in a variety of colours and compositions. </p> <p> The major alteration phase was determined to be amorphous opaline silica. Other species present are hematite and sulphur, with minor halides, sulphates and sheet silicate (chlorite). </p> / Thesis / Bachelor of Science (BSc)