AVO Logo
Site Map | FAQ |
Alaska Volcano Observatory
You are here: Home > Samples > Snyder_1959_3

SAMPLE INFO : Snyder_1959_3
Sample ID:Snyder_1959_3
Station ID:Snyder_1959_3
Sample Type 1:Lava
Field Lithology:Andesite
Text Description:
Andesite of Little Sitkin dacite. Color: medium gray (N 5). Texture: hypocrystalline, porphyritic with feldspar phenocrysts as much as 4 mm in diameter, and pyroxene phenocrysts as much as 3 mm long. Plagioclase megaphenocrysts, 20-30 percent, range from An35 to An56 and average An47; complex zoning and twinning common. Clinopyroxene, 8 percent, contains rare centers of orthopyroxene, 1 percent. Both unreacted olivine, 5 percent, and pyroxene are stained amber along joints. Magnetite, 2 percent, as anhedrons. Average composition of feldspar microlites in trachytic groundmass is An42.

Geology of Little Sitkin Island, Alaska