S&P/ASX 200 Index (ASX: XJO) mining stock Lynas Rare Earths Ltd (ASX: LYC) is taking a tumble today.

Shares in the $6.6 billion Aussie rare earths miner closed yesterday trading for $7.09. In morning trade on Friday, shares are changing hands for $6.70 apiece, down 5.6%.

For some context, the ASX 200 is down 0.1% at this same time.

As you can see on the chart above, Lynas shares remain up 11% over the past full year.

Here's what's moving the stock today.

ASX 200 mining stock slides on production update

The Lynas share price is sliding following the release of the miner's quarterly update for the three months ending 31 December (Q2 FY 2025).

The ASX 200 mining stock is under pressure despite a modest boost in gross sales revenue of $141 million over the quarter, up 3.7% year on year. Sales receipts came in at $146 million, up 36%.

On the mining front, Lynas produced 2,617 tonnes of rare earth oxide (REO), up 67% from Q2 FY 2024. And neodymium and praseodymium (NdPr) production of 1,292 tonnes was up 43%.

Meanwhile, cash payments for CAPEX, exploration and development declined by 23% year on year to $141 million.

As at 31 December, Lynas held $308 million in closing cash and short-term deposits.

What did management say?

Commenting on some of the highlights in Q2, Lynas Rare Earths CEO Amanda Lacaze noted that the ASX 200 mining stock officially opened its new Kalgoorlie Facility on 8 November 2024.

Lacaze said:

The opening highlighted the significance of our Kalgoorlie Facility as Australia's only downstream rare earths processing facility and the incredible achievement by all involved to construct, commission and commence operations of a facility of this scale and complexity in less than two and a half years from the receipt of full approvals.

The quarter also saw Lynas commission and integrate Stage 1 of its Mt Weld Expansion Project into operations as part of its 2025 growth plan.

Lacaze said Lynas achieved despite continuing low market prices.

"The revenue growth reflected our focus on high-value strategic customers and product mix and benefited from favourable foreign exchange rates," she said.

As for why the ASX 200 mining stock is likely under selling pressure today, Lacaze noted:

Quarterly production of total rare earth oxide (REO) production at 2,617 tonnes and NdPr production at 1,292 tonnes was lower than we had planned, reflecting very low production in December.