Figure 4. Relict, acicular aragonite crystals replaced by clear, sparry calcite identified in a chaotic vein in Sample 149-897D-17R-6, 62-65 cm. The matrix is composed of later botryoidal calcite, which has nucleated along the embayed face of the aragonite crystal and grown into open space between the crystals. A. Plane-polarized light photomicrograph displaying the radiating habit of calcite fibers in the botryoid and the equant habit of the replacement spar. B. Cathodoluminescence photomicrograph demonstrates the contrast in luminescent character of the two calcite generations. The luminescence of the botryoidal calcite is much higher than that of the spar, and exhibits an outward decrease in brightness. C. Interpretive sketch of same view.