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Example of resorption surfaces within a crystal of plagioclase feldspar (A-B).
Photomicrographs of magmatic potassium feldspar in some of the least altered rocks from the
Ok Tedi Intrusive Complex (C-F). Mantles of magmatic potassium feldspar on crystals of
plagioclase feldspar (G-H).
A. Photomicrograph of two crystals of plagioclase feldspar joined along a common face. One of
these has two internal resorption boundaries dividing it into three growth sectors (A, B, C Figure
26B). The outermost of these has a thin oscillatory zone at its outer edge Crossed-polar light.
The crystal cluster is about 1.6 x 2.2 mm. in size. DDH 319-339.3
B. Sketch of the crystals of plagioclase feldspar shown in A. DDH 319-339.3
C. Euhedral crystal of potassium feldspar in an andesine-potassium feldspar phanerite. The
crystal shows the typical frosted surface and uniform gray color of potassium feldspar. Several
subhedral or euhedral crystals of pyroxene abut against the crystal. The field of view is about
1.7 x 2.2 mm. Crossed-polar light. DDH 342-84.5.
D. Poikilitic texture. Chadacrysts of pyroxene and plagioclase feldspar enclosed in oikocryst of
potassium feldspar. This texture is magmatic in origin. The field of view is about 3 x 5 mm.
Crossed-polar light. Ok Tedi 1009.
E. Large single crystal of potassium feldspar. This crystal is among the largest found in suites 1
and 2 of petrographic analyses. Growth zones approximately parallel to the crystals faces can be
seen within the crystal. Alternatively this texture may be metasomatic. The field of view is about
4.7 x 7 mm. Plane polar light. DDH 303-243
F. Same phenocryst of potassium feldspar shown in E. Crossed-polar light. The crystal contains
several inclusions of plagioclase feldspar. These inclusions are aligned along growth zones
within the crystal of potassium feldspar or they may represent unreplaced portions of a partly
replaced feldspar of metasomatic origin.
G. Crystal of plagioclase feldspar overgrown by mantle of potassium feldspar. Both are euhedral
in shape and are elongated in the same direction. This texture is magmatic in origin. The field of
view is about 2.4 x 3.5 mm. Crossed-polar light. Ok Tedi 37.
