How do they do it? [3]: Out of a pile of rocks…

Goldfields landscapes are dotted with mullock heaps: and one of the curiosities of these heaps of apparently useless rock is that they often feature quite healthy trees. How can these trees get a foothold in material you definitely wouldn’t be spreading around your garden?

Eucalyptus nortonii [L]and Eucalyptus melliodora [R] on a mullock heap at Spring Gully: vegetation can colonise surprisingly unpromising locations, and mullock heaps are among the more surprising.

We put this question to Castlemaine geologist Julian Hollis, and he suggested that one answer might be that pyrites in the heaps decay to a soluble material called melanterite, an iron sulphate which is sometimes used as a fertilizer: so, contrary to what we might think, there are plant nutrients in these rock heaps. Julian was open minded about what other explanations there might be, however. Suggestions welcome.