MP Materials Corp. (MP) saw its stock price plummet 5.35% in after-hours trading on Wednesday, following the company's announcement of a proposed $500 million public offering of common stock. This sharp decline comes on the heels of a robust trading day, where the stock had earlier gained on positive news.

The rare earth materials producer, which had been riding high on recent positive developments, including a significant deal with Apple, now faces investor concerns over potential dilution of existing shares. The company stated that it intends to use the net proceeds from the offering for general corporate purposes, which may include capital expenditures, working capital, and potential acquisitions or strategic investments.

This after-hours drop contrasts starkly with the stock's performance earlier in the day. MP Materials had seen gains of over 5% in pre-market trading, buoyed by news of a $500 million deal with Apple for rare earth magnets and positive analyst coverage. The stock had even touched a record high in the previous session, reflecting strong investor confidence in the company's prospects in the growing rare earth materials market.

The proposed stock offering, while potentially providing MP Materials with additional capital for growth, has clearly spooked some investors in the short term. It remains to be seen how the market will digest this news in the coming trading sessions and what impact it may have on the company's long-term strategy and valuation.