Sample: Snyder_1959_12
| Sample ID: | Snyder_1959_12 [1] |
| Station ID: | Snyder_1959_12 |
| AT Num: | |
| Volcano: | Little Sitkin |
| Possible source: | |
| Eruption: | |
| Collector: | Snyder, G. L. |
| Date sampled: | |
| Sample type 1: | Lava |
| Color: | yellowish gray to medium light gray |
| Final unit: | |
| Text Description: | Rhyodacite of Pratt Point member of Little Sitkin dacite. Color: yellowish gray (5 P 7/1) to medium light gray (N 6). Texture: hypocrystalline, vesicular with "hairy" pumice developed locally, porphyritic with hornblende phenocrysts as much as 7 mm long and feldspar phenocrysts as much as 4 mm long. Plagioclase, 15-20 percent, ranges in composition from An27 to An50 and averages An40; sometimes poikilitic with inclusions of hornblende. Accessory minerals: oxyhornblende, 3-4 percent; hypersthene, 2-3 percent; quartz, 2-3 percent; magnetite, 1 percent. The quartz is characterized by conchoidal fractures and is very susceptible to plucking during grinding. The groundmass is about half small bubbles and half clear pinkish glass (N=1.490). The few plagioclase microlites average An39( ?). |
| Sample Location: |
References Cited
[1] Geology of Little Sitkin Island, Alaska, 1959
Snyder, G. L., 1959, Geology of Little Sitkin Island, Alaska: in Investigations of Alaskan volcanoes, U.S. Geological Survey Bulletin 1028-H, p. 169-210, 1 plate, scale 1:20,000.
full-text PDF 2 MB
plate 23 PDF 7 MB