The Geology and Petrography of Crater Lake National Park, 1902
PART II.
HYPERSTHENE-DACITES.
MINERAL COMPONENTS.
HYPERSTHENE.
This mineral is not as abundant as it is in the andesites, but it is never entirely lacking. It occurs in the same forms—namely, prism, two pinacoids, and flat terminal faces, in the same habits and with the same color, pleochroism, and inclosures of glass, etc., as it does in the andesites. The reader, therefore, is referred to the description of this mineral as given under the andesites on pp. 78 to 82. It could not be noticed that the pleochroism is less pronounced or the colors less deep than they are in the andesitic hypersthenes, so that there is no reason for considering these orthorhombic pyroxenes as enstatite rather than hypersthene. The crystals are mostly very sharp, although they may at times show some rounding of the corners. In only one case was a resorption noted, accompanied by the development of a dark, blackish-red, opaque rim (112).
