It's also the only volcano of it's kind in the world. The composition of it's lava is unique, it erupts at much cooler temperatures than regular lava and goes white as it solidifies and cools. This is natrocarbonatite, a chemical similar to washing soda. By day the lava looks grey, but by night it glows, revealing that, despite being cooler than other volcanoes, it is still far too hot to mess with.
The active crater. There is a second, inactive crater which provides an ideal camping ground for those studying the mountain. Previously camp was often set up in the active crater, but a series of accidents have made this less desirable. The crater has hornitos - small, active hills, scattered over it.
A fresh lava flow (black) runs over an old, solid flow (white).
By night the small eruptions look like those of a normal volcano, glowing red hot.
A daytime eruption of gaseous lava. It may look like mud, but this could give you severe burns.
I intend to visit Tanzania when time and money permit and climb this mountain so I can take a look into the crater.
Possibly the most comprehensive site on the mountain. Great photos!
EDIT : Pssst, mods. I think "Volcano" and "Ol Doinyo Lengai" would be more useful tags. :)