Nucor shares were halted for five minutes at 11:52 a.m. EDT after 100 Nucor shares traded at a penny each, a spokesman for the New York Stock Exchange said. The stock has spent most of the day between $39 and $40.

The hundred-shares-for-a-dollar trade triggered a so-called volatility trading pause, because it meant Nucor stock moved more than 10% (more like 99.9%, actually, but who’s counting) over a span of five minutes.

The stock reopened at 11:57 back in the $39-$40 range, down about 3% on the day.

Nucor shares have been under pressure following Tuesday morning’s announcement that the Charlotte, N.C., company expects a sharp decline in third-quarter earnings.

The NYSE spokesman said the bad trade took place on the CBOE Stock Exchange, or CBSX, a market operated by the Chicago Board Options Exchange.

Update: A spokeswoman there offered this account:

• CBSX received a large order for NEU.
• CBSX filled what it could (best price at the top of the book), sent the balance of the order to sweep the other exchanges for the best price. 
• Some of the shares could be executed on other exchanges, some could not.
• The balance of the order came back to CBSX (the originating exchange) and exhausted all interest in the CBSX book down to a penny.
• The “clearly erroneous” trades were busted.

Nucor’s brief trading meltdown comes at a time when the structure of the stock markets and the impact of computerized strategies like high-frequency trading are under heavy scrutiny by regulators.

The Financial Industry Regulatory Agency said Monday it hit one high-frequency trading firm and its workers with more than $2 million in sanctions for their attempts three years ago to manipulate the markets by entering and then withdrawing phantom orders.

Securities and Exchange Commission chief Mary Schapiro said last week the agency is investigating the origins and implications of the May 6 flash crash, which saw dozens of shares inexplicably plunge and then recover over a period of about 15 minutes. Regulators and exchange officials created single-stock trading halts for stocks that make sudden moves in the wake of that incident, and the rules have now been invoked a handful of times.

Nucor said in its press release the summer’s slowdown confirms the economy “has entered into a new period of uncertainty.” Unfortunately, it seems the same might be said about the markets.