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When a US department store decided to start selling a stone for $85 (£65), people were - somewhat understandably - shocked.

To be fair to Nordstrom, the stone came in a fetching leather pouch and was undeniably popular with its clientele, selling out in both large (and small) within days.

But while the rest of humanity decried the extravagance as proof the Western world was rapidly heading the way of the Roman Empire, one Wisconsin paediatrician saw it slightly differently.

Dr David Margolis, a cancer specialist at the Children's Hospital of Wisconsin, Milwaukee, looked at Nordstrom and thought, there might be something in this - although with far less emphasis on ostentatious consumerism.

"I kind of thought instead of rocks in leather, it could be rocks for a reason," Dr Margolis explained, the gem of an idea beginning to form.

"Children's Hospital Wisconsin is where I've worked for a long time and I think that people helping other people is what this season's about."

In fact, Dr Margolis mainly saw an opportunity because he knew there were plenty of good, free stones down on the shore of Lake Michigan.

After he spent his day off collecting as many as possible, the hospital unveiled their latest fundraising campaign: donate $85 to the hospital, and you will get your own stone in the post.

And it seems that stones are this year's hot item.

While Dr Margolis's offerings may not have the leather pouch or be made from "smooth Los Angeles-area stone", they do promise to help provide life-saving care and research into illnesses for Wisconsin's youngest residents, and so have been flying out the office.

So far, more than 150 people have , raising more than $20,000 (£16,000). And with people queuing up to donate stones, the hospital is hoping for more orders before the 31 December end date.

"We are just having fun," Dr Margolis said on Monday. "It's been really cool to see friends from grade school, former patients reaching out, and people who are complete strangers. I just think it touched a nerve."