In XN, the radial nature of the quartz is much more obvious. See below for more detail. Also note the concentric light and dark variations, caused by very slight changes in the orientation and size of the quartz crystals as they grew. Note that these patterns match between each of the radial quartz growths. This occurs because the variations in growth were likely caused by chemical changes in the solutions precipitating the quartz, which would simultaneously affect the growth of the crystals around the entire cavity.
Arrows point to the black, opaque pyrite rim.
Note the way the quartz growths preferentially nucleated on projections in the pyrite rim. Closer view of one of the radial growths of quartz, resolving individual needle-like quartz crystals. This cavity is completely infilled with blocky calcite crystals. In PPL, the high relief of calcite makes the crystal boundaries obvious. In XN, the crystals are brighter or darker depending upon their orientation with respect to the polarizers.