Figure F31. The spheroidal texture observed in hand specimen of Unit 31 (interval 193-1188F-6Z-1, 45-47 cm) (see Fig. F23, ) is reflected by round to bulbous, coalesced brown domains surrounded by gray, cristobalite-rich groundmass in thin section. A. Brown spheroidal domains outlined by dark brown rims, which also encircle individual spheroids in coalesced aggregates. Arrow = coalesced spheroids (in plane-polarized light; width of view = 5.5 mm. Photomicrograph ID# 1188F_16; thin section 67). B. The spheroids consist of very fine, randomly oriented plagioclase needles. However, locally radiating crystal aggregates can be observed in the center of these structures (in plane-polarized light; width of view = 0.7 mm. Photomicrograph ID# 1188F_18; thin section 67). C. The generally feltlike internal texture of the spheroids and a small central domain with radiating crystal aggregates can be recognized using crossed polarizers and the condenser lens (in cross-polarized light; width of view = 0.7 mm. Photomicrograph ID# 1188F_19; thin section 67). D. The groundmass between the spheroids consists dominantly of fine-grained cristobalite; however, there are some coarser crystal aggregates that are attached to the outer surface of the spheroids (in cross-polarized light; width of view = 1.4 mm. Photomicrograph ID# 1188F

Figure F31. The spheroidal texture observed in hand specimen of Unit 31 (interval 193-1188F-6Z-1, 45-47 cm) (see Fig. F23) is reflected by round to bulbous, coalesced brown domains surrounded by gray, cristobalite-rich groundmass in thin section. A. Brown spheroidal domains outlined by dark brown rims, which also encircle individual spheroids in coalesced aggregates. Arrow = coalesced spheroids (in plane-polarized light; width of view = 5.5 mm. Photomicrograph ID# 1188F_16; thin section 67). B. The spheroids consist of very fine, randomly oriented plagioclase needles. However, locally radiating crystal aggregates can be observed in the center of these structures (in plane-polarized light; width of view = 0.7 mm. Photomicrograph ID# 1188F_18; thin section 67). C. The generally feltlike internal texture of the spheroids and a small central domain with radiating crystal aggregates can be recognized using crossed polarizers and the condenser lens (in cross-polarized light; width of view = 0.7 mm. Photomicrograph ID# 1188F_19; thin section 67). D. The groundmass between the spheroids consists dominantly of fine-grained cristobalite; however, there are some coarser crystal aggregates that are attached to the outer surface of the spheroids (in cross-polarized light; width of view = 1.4 mm. Photomicrograph ID# 1188F_26; thin section 67).