October Microphoto of the Month
Zoned hornblende, Mid-Atlantic Ridge. The brown, titanium-rich hornblende in the core of the crystal crystallized from a magma at high temperature, between 900 and 1000 degrees celsius. As the magma cooled and changed composition, the titanium-poor, tan-colored hornblende crystallized at the rim of the crystal. The straight line contacts between the brown and tan hornblende are crystal faces. They crystal is approximately 2 mm in length.