Interesting off-beat find via kris de kecker’s No Tech Magazine, which today linked to WIKI-style and PDF versions of Klaus Grasser and Gernot Minke’s 1990 book Building With Pumice. Turns out pumice, a foamy igneous rock, often tan in color and generally known for its ability to float in water, is both plentiful, in many parts of the world, and has many desirable properties as a concrete aggregate and/or as a solid block material. A bit dry, perhaps (ba-bing!), but interesting reading for alternative construction enthusiasts.
In other words, it is a lot like AAC (Aerated Autoclaved Concrete)