Ian Larsen's collection of glow-in-the-dark crystals at the Taranaki Lapidary and Mineral Club's biennial show.

The urge to collect rocks is, apparently, easily caught.

A visit to the Taranaki Lapidary and Mineral Club's last show triggered a new hobby for Elliot Alford, 12, who is now the club's youngest member.

Over the weekend, Elliot had his own carefully-curated cabinet of rocks and gems from around the world on display as part of the club's biennial show in New Plymouth.

ANDY JACKSON/STUFF Elliot Alford, 12, with his display of rocks and gems.

"I went to look at the rock show two years ago, then started going to the club to learn to polish all my rocks," he said.

Many of the stones and gems were given to him, he said, and he'd bought a few too.

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ANDY JACKSON/STUFF Trevor Gillum works on polishing a rock into a gem.

Crowds thronged the Spotswood College hall to admire the displays, buy jewellery and stones and watch club members using machines to grind and polish rough, raw rocks to reveal the gemstones hidden inside.

In one corner, children tried to get polished stones out of a block of ice with frozen fingers, while adults rummaged through another pile of rocks marked 'make an offer'.

Under a black-shrouded gazebo, Ian Larsen had a table displaying a bunch of crystals that looked quite plain under normal light, but glowed luminous green, pink, red and gold when he switched on a black light.

ANDY JACKSON/STUFF Polishing a rock is a slow process.

"The green ones have a small amount of uranium in them. I told one visitor this and she quickly left the tent, but I've had them tested by a geiger counter and they are apparently about four per cent of being dangerous," he said.

Club secretary Hazel Madgewick said she was lured into lapidary 17 years ago when she went to a show and her neighbour talked her into becoming club secretary.

"I didn't know the first thing about it. Now I have five cabinets [of rocks and gems] in my lounge and the garage is lined with them too."

ANDY JACKSON/STUFF Club secretary Hazel Madgewick surveys the busy show hall on Saturday.

The club was very social, gathering every two weeks to polish and grind rocks and stones, and also going on club trips to other clubs and shows around the country.

There were dealers and collectors from all around the country at the Taranaki show, she said.