Silver prices have been on a bit of a rollercoaster, bottoming out in December 2015, when prices for the metal dropped to just $13.71 per ounce. Silver seemed to be on a path to recovery by mid-2016, trading just above $20 per ounce in July and August before settling into its 2017 level of around $17.

Despite its volatility, however, silver remains a consistently attractive investment for people who want exposure to precious metals. It has far more industrial applications than gold, which means that silver stands to gain in a growing economy. If you are betting on economic growth, especially in the manufacturing and industrial sectors, silver may be a good option. (See also: How Will Trump's Victory Boost Silver?)

Of course, owning physical silver isn't the only way to get a piece of the silver market. Silver mining and exploration companies offer an indirect way to enter the market. Many silver mining companies have seen significant volatility over the past few years. In 2017, several have reported substantial gains with momentum expected to carry over into 2018. Here's a look at four silver penny stocks for you to consider. These stocks offer investment at a low entry share price. (See also: Top 3 Silver ETFs for 2017.)

Note: Stocks were chosen based on performance, revenue and a trading price below $5.00. Data is as of December 19, 2017, unless otherwise noted.

Bunker Hill Mining Corp. (BHLL)           

The Bunker Hill Mining Corp. has its headquarters in Toronto, Ontario, Canada. The company has been in the mining business since 2007. Its business includes mining for copper, gold and silver. The company operates the Bunker Hill Mine which is located in Kellogg, Idaho in the Coeur d’Alene Basin.

In November 2016, the company began negotiations to acquire the Bunker Hill Mine Complex. Subsequently in September 2017, the company changed its name from Liberty Silver Corp. to Bunker Hill Mining Corp. Its stock trades as BNKR on the Canadian stock exchange and BHLL in the U.S.

For the period ending December 19, 2017, the company’s stock has reported a 1,800% increase with a gain of $1.26. As of December 19, 2017 it was trading at $1.33. The company has halted operations through the Bunker Hill Mine Complex acquisition but expects to reopen in the near-term. In steady state production the company estimates it will produce approximately 1,500 tons per day.

Americas Silver Corp. (USAS)

Americas Silver Corp. has gained 27.56% over the past year. It is trading at $3.56. The company has a market cap of $144.4 million. Its trailing 12-month revenue is $56.63 million and it has managed to generate cash flow from operations of $3.33 million over the past 12 months.

The company is based in Canada. It has two primary operating facilities in the Americas, the Galena Complex in Idaho and the Cosala Operations in Sinaloa, Mexico. It is also developing a new mining operations site, the San Felipe project in Sonora, Mexico. The company has been significantly reducing costs with a $5 per ounce silver cash cost expected for 2017 compared to $10 per ounce in 2016. Production is also expected to be up with guidance of 5.0 to 5.5 million ounces expected for 2017 compared to 4.7 million ounces in 2016.

Silvercorp Metals Inc. (SVM)

Silvercorp continued to remain one of the top silver producing companies through 2017. The company reported a one year return of 9.33%. Its trailing 12-month revenue is $169.14 million, generating cash flow from operations of $70.82 million and free cash flow of $35.19 million.

Based in Vancouver, Canada, the company primarily operates mines in China throughout the Ying Mining district. It is China’s largest publicly traded silver producer with 6.5 million ounces of silver produced in fiscal year 2017. The company also has plans for new mining of silver, lead and zinc at its newest production base, the Guangdong Province in China.

Hecla Mining (HL)

Hecla Mining has also shown potential for growth in 2018. The company is currently trading at $3.94. It reports one of the highest revenue levels in the silver mining industry. For the trailing 12 months it had revenue of $581.9 million. Free cash flow from operations for the trailing 12 month period was $126.33 million and free cash flow was $11.39 million.

The company has its headquartered in Coeur d'Alene, Idaho. It operates four gold and silver mines in Alaska, Mexico and Canada. It also mines for lead and zinc. Its primary silver properties are the Greens Creek, Lucky Friday and San Sebastian mines. Hecla is the largest silver producer in the U.S. and the oldest precious metals mining company on the New York Stock Exchange.