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A. Patchwork aggregate pseudomorph of hydrothermal biotite after a magmatic
ferromagnesian mineral. Shows the pale yellow to orange pleochroism typical of
hydrothermal biotites from the altered rocks at Ok Tedi. The field of view is
about 4.6 x 6.6 mm. Crossed-polar light. DDH 355-382.5
B. Anhedral crystals of hydrothermal biotite in a potassium feldspar-altered
phanerite. These crystals show uniform pleochroism and birefringence and are
oriented so as to display their maximum pleochroic color (pale orange brown).
The field of view is about 0.8 x 1.2 mm. Plane-polar light. JDD-94-14
C. Patchwork aggregate pseudomorph of hydrothermal biotite, quartz, and opaque mineral after a magmatic ferromagnesian mineral. The field of view is about 0.8 x 1.2 mm. Plane-polar light. DDH 345-468
D. Patchwork aggregate pseudomorph of hydrothermal biotite and quartz after a magmatic ferromagnesian mineral. The linear streaks in the quartz (pale yellow) are probably fluid inclusions. A rounded crystal of zircon can be seen in near the center of the right edge of the photograph. The field of view is about 4.5 x 6.7 mm. Crossed-polar light. DDH 345-468
E. Pseudomorph of hydrothermal biotite after a phenocryst of hornblende in hornblende porphyry. The euhedral shape of the original crystal is retained. The secondary biotite has a felted texture. The field of view is about 0.7 x 1.0 mm. Plane-polar light. JDD-94-05
F. The same pseudomorph of hydrothermal biotite after hornblende shown in E. An inclusion of plagioclase feldspar can be seen in the upper right part of the pseudomorph. Crossed-polar light. JDD-94-05
G. Pseudomorph of hydrothermal biotite after hornblende in hornblende porphyry. Shows maximum and minimum pleochroic colors of the hydrothermal biotite (medium orange brown - large crystal; pale yellow brown - smaller crystal included within the larger one). The field of view is about 2 x 3 mm. Plane-polar light. JDD-94-05
H. Pseudomorphs of hydrothermal biotite after ferromagnesian minerals in a sample of texturally destroyed rock. The secondary biotite is dark brown in color. Identification of the original magmatic minerals is uncertain. The field of view is about 4 x 6 mm. Plane-polar light. DDH 366-226.5
