Igneous texture
Zoning texture
Changes in color or extinction angle from core to rim in a solid-solution mineral. Oscillatory zoning shows concentric rings of different extinction angle and interference color.
What it means
Incomplete reaction between melt and crystal. Plagioclase is normally zoned from calcic cores to sodic rims; reverse zoning can record mixing with more primitive magma.
Where to look for it
Plagioclase in andesite, basalt, rhyolite; also pyroxene, olivine, hornblende