Inside an independent gemstone store in Sydney's inner-west, customers politely edged around each other while fingering the glittering rocks on display.

Key points: Some stones sold as wellness crystals online have been traced to mines involved in unethical practices.

Some stones sold as wellness crystals online have been traced to mines involved in unethical practices. Studies have found "healing" crystals do not perform better than placebos

Studies have found "healing" crystals do not perform better than placebos Some owners of crystal stores are now ensuring they source ethical stones.

On a quiet mid-week afternoon, there were more than 10 customers packed into the small shop, studying the array of crystals, gemstones, and rocks.

There was even a piece of Mars and a sliver of the moon for sale — though with price tags of up to $10,000, those are a little out of the price range of the typical customer.

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One of the shop's gem-seekers was a yoga teacher called Anita, who stood in front of a wall of coloured stones, waiting for the right crystal to speak to her.

"What generally happens is that I'll find a stone that I want, and when I look up its properties later it will be exactly what I need in life," she said.

"The crystal chooses you."

The crystal business certainly seems to have chosen Mineralism owners Jed Underwood and Jess Lahoud.

Ms Lahoud is practically gemstone royalty, spending her childhood mining opals in the Australian outback with her family.

She met her co-owner, now her husband, at a gemstone expo in the middle of the desert and the couple founded Mineralism four years ago.

Jed Underwood sells crystals at a Sydney store. ( ABC News: Scott Mitchell )

They source their stones worldwide, including from Africa, South America and Morocco, and say all the stones in their store are ethically sourced.

"We try hard to make sure we know the people who are finding them," said Mr Underwood.

"We don't want to sell a stone for a healing purpose but it has a really dark past to it."

Where do the crystals come from?

The dark past of healing crystals is exactly what interested Emily Atkin, a New Republic writer who has been investigating the industry.

"The first thing I thought was, 'so that is a rock, so it was mined somewhere, right? So, what kind of mine does a healing crystal come from?"

Emily Atkin wrote about the ethical pitfalls of some wellness crystals for The New Republic. ( Supplied: Twitter )

But the truth about the origins of healing crystals was shadier than she could have imagined.

"That question just sent me down this spiral of mystery," she said.

Ms Atkin's investigations into the billion-dollar healing crystal industry focused mainly on stones supplied online and in the US.

"I would say that the majority of people who sell crystals online actually don't know where their crystals come from," she said.

When she traced their origins herself, she found many crystals are the by-products of large-scale industrial mines for things like gold and copper.

"Those mines are not your most environmentally friendly places," she said.

Ms Atkin discovered a crop of stones from a mine in Utah which had been cited multiple times for polluting the drinking water of Indigenous communities.

Then there's the issue of child labour.

Some stones prized in the crystal community can only be found in certain parts of the world, places that have lax mining regulations for children and child labour.

"So you might be getting a stone from the Democratic Republic of Congo and you might not know if a 12-year-old mined it or not," she said.

"It's just something to consider if you're using a healing crystal to connect yourself with the earth, at what price did the earth pay for you to get it."

Do crystals have healing properties?

At Mineralism in Sydney, Mr Underwood and Ms Lahoud estimated that 70 per cent of their customers bought crystals for their supposed healing properties.

The properties of crystals for "healing" have been the subject of several studies. ( ABC News: Scott Mitchell )

It's worth noting that crystals have no proven healing effects, according to Dr Andrew Christy, the senior curator of minerals at the Queensland Museum.

That's not for lack of trying though, said Dr Christy, who cited several studies, including one into rose quartz about 20 years ago.

"A researcher in London took a group of about 80 people, split them into two, gave half of them real quartz crystals and half of them glass fake crystals," he said.

"(They) got them to report any experiences they had while handling them.

"They found no statistical difference between the two."

But Mineralism customers, like Deepa who was shopping for some "basic" amethyst and quartz for her home, begged to differ.

"Quartz is a good general healing crystal, and amethyst is good for your spiritual side and health," she said.

One customer insisted that quartz was a good "healing" crystal. ( ABC News: Scott Mitchell )

Deepa said she has slowly become more aware of the origins of the crystals she buys.

"Initially I wasn't, but you want to know they've been ethically sourced," she said.

Yoga teacher Anita admitted she doesn't always check where her stones come from (she has 40 at home), but said as long as the crystals are cleansed they can have good energy.

"It's going to sound crazy, are you sure you want to put this on a mainstream website?" She asked.

"Well, you cleanse them with sage or you can energetically clean them with Reiki."

While Anita thought buying ethically-sourced stones was a good idea, she saw the issue as more of a first-world problem.

"This is like the third wave — first it was like 'where does your food come from?' Then 'where do your clothes come from?'

"Now it's 'where do your crystals come from?'"