"At first I thought it was an odd looking rock. I'm quite fascinated with odd bits of metal which come across the screen and when I had a closer look I saw it was rusted.
"It's not big and definitely not a mine, but I hope History House can work out what it actually is and what it was used for."
The majority of nzherald readers who chimed in on the debate thought it was a cannonball, with one reader suggesting it was French in origin, while another suggested it was used in the land wars between British colonialists and Maori.
Others thought it was a mace - but most provided no explanation as to why a medieval weapon might turn up in a West Coast shingle pit.
One of the more inventive suggestions was that the ball was used to play bocce volo - an Italian bowling game in which players toss metal balls, similar to petanque. The reader cited the characteristic dimples protruding from the ball as evidence.
Other suggestions included that it was a meteorite, a chimney cleaning weight, a land marker, the ball from a prisoner's ball-and-chain, or a water-pump handle counterweight.
But perhaps the most likely suggestion, put forward by several readers, was that the rusted ball was used for quarrying or mining - a theory that seems to accord with where the ball was located.
One reader said it was likely a grinding ball used in a ball mill, which are used to grind up rocks into powder, often at gold mines.
Another reader said: "Looks like grinding media from a mine. You put these inside a mill to help crush rock. We have similar sized ones at the mine where I work but without the dimples."
Similar grinding balls were used in the limestone industry, another reader said: "Remember seeing drums of them at the lime crushing works in Oamaru when I was younger."
Mystery solved?
