Kingdom: Fungi
Division: Ascomycota
Subdivision: Pezizomycotina
Class: Sordariomycetes
Subclass: Xylariomycetidae
Order: Xylariales
Family: Xylariaceae
Genus: Daldinia
Species: D. concentrica
Binomial name Daldinia concentrica
Common names: King Alfreds Cakes, Cramp balls,

These always grow on wood. They look and feel like hard half-round balls.
When cut in half, concentric bands of light and dark colours are seen. See photo below

This fungus is a useful form of tinder for fire-lighting. It does need to be completely dry, whereupon it will easily take a spark. It burns slowly, much like a charcoal briquette, with a particularly pungent smoke. Once lit it is quite difficult to extinguish but fragments can be broken off and transferred to a tinder ball to create an open flame. Maoris used to cart fire from one place to another using this fungus, 
A video on its use in firefighting can be found at the bottom of this page.


Daldina concentrica grown on an old log
[1]

[2] 

[3]

[4]

Daldina concentrica cut  in half showing the concentric bands

The following fungi of the same genus and to date unable to identify.[5] 

A video on identifying Daldina concentrica and its use as a firefighter.
VIDEO

Thanks to Wikipedia for text and information http://creativecommons.org/licenses/by-sa/3.0/