Figure F68. A. Partially altered glass fragment rimmed by brown smectite with larger vesicle (left) filled by brown smectite and smaller empty vesicle (right) in Sample 192-1184A-45R-6, 82-85 cm. The interfaces between smectite and fresh glass are characterized by "hairy" brown channels filled with smectite that possibly formed by microbially mediated alteration of the glass (field of view = 1.4 mm; plane-polarized light; photomicrograph ID# 1184A_152). B. High magnification photomicrograph of glass fragment shown in (A) (upper center portion) showing two distinct types of possible microbially mediated alteration features. String-of-pearls channels (center left) are characterized by spherical cavities joined by thin channels, whereas smooth-walled, gently curved channels (right) appear to be generally free of clay minerals and are possibly still open (Sample 192-1184A-45R-6, 82-85 cm; field of view = 0.28 mm; plane-polarized light; photomicrograph ID# 1184A

Figure F68. A. Partially altered glass fragment rimmed by brown smectite with larger vesicle (left) filled by brown smectite and smaller empty vesicle (right) in Sample 192-1184A-45R-6, 82-85 cm. The interfaces between smectite and fresh glass are characterized by "hairy" brown channels filled with smectite that possibly formed by microbially mediated alteration of the glass (field of view = 1.4 mm; plane-polarized light; photomicrograph ID# 1184A_152). B. High magnification photomicrograph of glass fragment shown in (A) (upper center portion) showing two distinct types of possible microbially mediated alteration features. String-of-pearls channels (center left) are characterized by spherical cavities joined by thin channels, whereas smooth-walled, gently curved channels (right) appear to be generally free of clay minerals and are possibly still open (Sample 192-1184A-45R-6, 82-85 cm; field of view = 0.28 mm; plane-polarized light; photomicrograph ID# 1184A_154).