Francesca Fontana

Well,

Exchange operator CME Group increased margin requirements to ensure traders put down more cash on their bets, which CME and its peers typically do after price run-ups in commodities.

And on Monday, shares of silver specialist Hekla Mining fell 5%, while shares of the gold mining giant Newmont fell 5.6%.

And on a weekly basis, Hekla ended down 6.6%, while Newmont fell 4.3%.

So while I spent my holidays here in New York, those of you who traveled by air probably already have a good understanding of why some airline stocks were falling on Monday.

Just in time for the year-end travel rush, holiday snowstorms across the U.S.

caused a flurry of cancellations ahead of the new year.

After a weekend of chaotic travel, on Monday, more than 10,000 U.S.

flights were delayed, according to flight data specialist FlightAware.

more than 900 flights within, into, or out of the U.S.

were canceled.

And so we saw, for instance, Delta Airlines shares fall 1.9% Monday, while American Airlines also lost 1.9%, and United Airlines fell 2.3%.

On a weekly basis, Delta lost 2.5%, United ended down 0.9%, and American ended up about 0.3%.

Finally, Elon Musk's Tesla is having a rough start to the new year, as a Chinese rival took its crown as the world's biggest seller of electric cars.

On Friday, Tesla reported that its annual deliveries fell 8.6% from the year before to roughly 1.6 million vehicles.

Chinese auto company BYD, meanwhile, sold 2.26 million electric vehicles.

It's certainly a reversal of fortunes for these two.

Tesla was once the leading EV maker, while only a few years ago, BYD's founder worried that the company might not survive.

So how'd Tesla's shares do?

The stock ended up dropping 2.6% on Friday and notched a weekly loss of 7.8%.