hugh walters

A hardcover book from the Sixties (read it in the library). A probe to Venus returns a sample and it crashes in the (Sahara?) Desert. A caravan comes across it and is consumed by the mold. Later the site is again discovered and the mold carried to the rest of the world where it begins spreading...

I was mid teens when I started reading the Chris Godfrey series by Hugh Walters so a bit late. I think they were written for the 11 - 13 ages, they were, I think (should really have Googled this before starting this thread) written in the fifties and sixties. The protagonist is a 17 year old...