An alkali feldspar intermediate between low sanidine and high albite. A strange, elongated crystal of anorthoclase without matrix, showing modest twinning, here from a well-documented
and sought-after locality for this feldspar-group mineral. From an old stash collected circa 1960. Mt. Erebus Volcano (3794m) is home to the world?s only persistently convecting anorthoclase-phonolite lava lake. There is only one other place on the planet where these crystals can be found, Mt. Kenya, Africa. Crystals grow in the magma beneath Erebus and get spit out of the mountain inside glassy volcanic bombs. The glass quickly weathers away leaving the mountainside covered in crystals. These crystals are coveted by almost everyone at McMurdo Station.
