Shares of Cliffs Natural Resources Inc (CLF - Get Report) were slumping, down 5.21% to $3.37 on heavy volume in afternoon trading Tuesday, along with other steel related stocks amid the slump in iron ore prices.

Iron ore, one of the main raw materials to make steel, was down 5.12% to $49.60 a tonne, according to a price index compiled by Metal Bulletin. The index fell below the $50 level for the first time since April 16.

Yesterday, data showed that inventories at Chinese ports increased by 2.8% last week to 81.55 million tons following 11 straight weeks of declines, Bloomberg reported.

The rebound in Chinese port stockpiles are weakening iron ore prices as big miners increase production and demand slows, according to Bloomberg.

About 8.51 million shares have changed hands as of 12:52 p.m. ET today, compared to its average trading volume of about 7.89 million shares a day.

Cleveland, Ohio-based Cliffs Natural Resources is an international mining and natural resources company.

The company is an iron ore producer and a producer of metallurgical coal with its operations organized according to product category and geographic location.

In the U.S., Cliffs operates five iron ore mines in Michigan and Minnesota, five metallurgical coal mines located in West Virginia and Alabama and one thermal coal mine located in West Virginia.

Separately, TheStreet Ratings team rates CLIFFS NATURAL RESOURCES INC as a Sell with a ratings score of D-. TheStreet Ratings Team has this to say about their recommendation:

"We rate CLIFFS NATURAL RESOURCES INC (CLF) a SELL. This is driven by a few notable weaknesses, which we believe should have a greater impact than any strengths, and could make it more difficult for investors to achieve positive results compared to most of the stocks we cover. The company's weaknesses can be seen in multiple areas, such as its deteriorating net income, poor profit margins, weak operating cash flow and generally disappointing historical performance in the stock itself."

Highlights from the analysis by TheStreet Ratings Team goes as follows:

-The company, on the basis of change in net income from the same quarter one year ago, has significantly underperformed when compared to that of the S&P 500 and the Metals & Mining industry. The net income has significantly decreased by 980.8% when compared to the same quarter one year ago, falling from -$70.30 million to -$759.80 million.

-The gross profit margin for CLIFFS NATURAL RESOURCES INC is rather low; currently it is at 24.80%. It has decreased significantly from the same period last year. Along with this, the net profit margin of -170.35% is significantly below that of the industry average.

-Net operating cash flow has significantly decreased to -$228.20 million or 178.29% when compared to the same quarter last year. In addition, when comparing to the industry average, the firm's growth rate is much lower.

-CLF's stock share price has done very poorly compared to where it was a year ago: Despite any rallies, the net result is that it is down by 71.94%, which is also worse that the performance of the S&P 500 Index. Investors have so far failed to pay much attention to the earnings improvements the company has managed to achieve over the last quarter. Naturally, the overall market trend is bound to be a significant factor. However, in one sense, the stock's sharp decline last year is a positive for future investors, making it cheaper (in proportion to its earnings over the past year) than most other stocks in its industry. But due to other concerns, we feel the stock is still not a good buy right now.