Figure F51. Photomicrographs in plane-polarized light of an interval that is associated with high magnetic susceptibility near the top of Unit 3 (Sample 210-1276A-15R-4, 136-138 cm). A. Large, subrounded volcanic clast in upper right corner is composed of colorless glass (C) with plagioclase microlites (P) and an isolated vesicle (V). The surrounding matrix includes biotite (B) and quartz (Q). B. Concentration of smaller opaque minerals (O) and large, mostly euhedral quartz crystals (Q) within a lamina. Given the high magnetic susceptibility of this interval, the opaque minerals are probably magnetite.

Figure F51. Photomicrographs in plane-polarized light of an interval that is associated with high magnetic susceptibility near the top of Unit 3 (Sample 210-1276A-15R-4, 136-138 cm). A. Large, subrounded volcanic clast in upper right corner is composed of colorless glass (C) with plagioclase microlites (P) and an isolated vesicle (V). The surrounding matrix includes biotite (B) and quartz (Q). B. Concentration of smaller opaque minerals (O) and large, mostly euhedral quartz crystals (Q) within a lamina. Given the high magnetic susceptibility of this interval, the opaque minerals are probably magnetite.