Gold inspires strong emotions from investors both for and against investing in the precious metal, and yesterday's $130-per-ounce drop in the price of gold has reawakened the debate about whether gold is a smart investment.

Yet forgotten in the turmoil that hit gold yesterday was the fact that many other commodities also suffered big declines. On the heels of China's slowing growth, the fact that many metals besides gold took substantial hits points to a more important trend that has greater implications for stock market investors and the global economy overall. Let's take a look at some of the largely ignored commodities that saw devastating declines yesterday.

1. Copper
Copper prices didn't fall nearly as much as gold, with near-month futures falling by around 2% yesterday. Yet the drop pushed copper to its lowest levels since late 2011, with the price having fallen by 14% just since early February.

China is responsible for about 40% of the world's copper consumption, so a slowdown there bodes ill for world demand. But one key element with copper is the increase in supply, with major players Freeport-McMoRan Copper & Gold (NYSE:FCX) and Southern Copper (NYSE:SCCO) among companies trying to spur production growth in the metal. With copper often acting as a barometer of overall industrial activity, its drop has far more troubling implications for views on global growth than gold's crash.

2. Aluminum
Aluminum prices fell to three-and-a-half-year lows during trading in London yesterday. Yet unlike copper, which remains profitable for companies that produce it, aluminum has strained major producers' profit margins for years now. According to one estimate, about a quarter of all aluminum companies around the world are losing money at current prices, and with further declines, that trend is likely to increase.

Alcoa (NYSE:AA) has attempted to weather the storm by trying to think long-term, implementing strategies that assume an eventual recovery in the aluminum market. Yet the longer the current weakness lasts, the harder it will be for Alcoa to maintain its confidence in the future.

3. Silver
Among precious metals, silver often gets left out. But silver's 11% decline yesterday to a two-and-a-half-year low was even more extreme than gold's crash.

Silver serves a mixed role for investors. In some ways, it acts as a cheaper investment vehicle to gold for pure trading purposes. Yet silver also has industrial applications, including electronics, traditional photography, mirrors, and medical purposes. A lack of demand for silver therefore has deeper implications for the overall economy, and combined with the pressures that silver miners share with their gold counterparts in terms of cost, times could be tough for mining companies in the near future.

4. Platinum-group metals
Platinum and palladium both fell sharply, losing 5% and 6% of their value, respectively. Those losses weren't as extreme as gold's, but they nevertheless represented a drop to levels not seen since late last year. The two major miners producing the white metals, Stillwater Mining (NYSE:SWC) and North American Palladium (NYSEMKT:PAL), both lost more than 10% on the day.

Platinum-group metals are much rarer than gold and therefore more prone to supply disruptions, with labor strife in South Africa having led to short-term price spikes on many occasions in recent years. Their major industrial use is in automobile catalytic converters, and with the auto industry having been healthy lately, the white metals have outperformed gold all year. That trend may continue even if the prevailing direction throughout metals is down.

5. Oil
Oil isn't usually linked to gold, but as a reflection of economic demand, the $4 drop in the price of oil today is consistent with the behavior of precious and industrial metals. The drop may prove good for consumers who have had to pay high gasoline prices lately, but given the reliance on the booming energy industry for economic growth throughout the U.S., lower prices that threaten profits for energy companies could have a net negative impact on the economy.

Don't forget these markets again
Gold will likely keep getting all the headlines for the foreseeable future. But keep your eye on these forgotten markets. That way, you'll be able to see if gold's behavior is an outlier or if the rest of the commodities market is following its lead.

Fool contributor Dan Caplinger owns shares of Freeport-McMoRan Copper & Gold. You can follow him on Twitter @DanCaplinger. The Motley Fool owns shares of Freeport-McMoRan Copper & Gold. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.