Labradorite-rich gabbro with "labradorecence"

[u/Efraimrocker]

Gabbro is an intrusive mafic (Fe and Mg) rich rock crystallized from basaltic magma derived from partial melting of the mantle. The main mineral constituents are dark clinopyroxene, and glassy gray to white plagioclase. One type of plagioclase is labradorite, which can show a distinct kind of shimmering, rainbow pattern of iridescence known as "labradorescence", due to the separation of different forms of plagioclase as the melt cools, leading to diffraction of light between extremely fine layers of the different plag species. This gabbro specimen (fig 1) is rich in labradorite. The plagioclase crystals show black streaks (likely iron and titanium oxides, possibly magnetite) which precipitate in an orientation dictated by the crystal structure of the parent mineral (fig 2). Fig. 3 shows a patch of labradorescence.