Sensational Rock Formations: Moeraki Boulders

We are opening new series of "sensational rock formations" found throughout the Earth: this is the first part; send us tips about other incredible rock shapes, we will cover them in next installments of the series.
Strangely Round Rocks of "Unknown Origin"
Well, saying "unknown origin" is an obvious exaggeration, since it is widely assumed that they must be sedimentary concretions, and were created by cementation of mud stone, coastal erosion, time and elements, just like any other unusual rock formation.
Yet their bizarre cracked shells, often perfectly spherical shape and unexpected locations remain largely unexplained and keeps them regarded as a "geological mystery". Not to mention other theories: are they fossils? alien eggs? weird energy storage devices from a crashed alien ship? Some even say that they are the... Great Balls of Fire (that fell down on Earth in Biblical times).

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