Lately, the stock market has captured the lion's share of investors' attention, especially as it climbed to successive all-time record highs. But the crash of gold prices has taken on greater significance today, losing more than $100 per ounce today alone and adding to similar declines over the past couple of weeks. Moreover, as investor confidence is deflated by a report from China suggesting slower growth in the emerging-market country as well as a poor reading on sentiment among homebuilders, the Dow Jones Industrials (^DJI -0.11%) opened the week with losses that quickly widened to more than 100 points before recovering slightly. As of 10:45 a.m. EDT, the Dow is down about 70 points.

Among Dow stocks, the obvious victim of gold's decline is Caterpillar (CAT 0.07%), which has dropped 2.7%. The maker of construction and mining equipment will suffer both from slowing growth in China, one of its primary markets, and from reduced mining activity among gold producers that will suddenly find their operations much less profitable than they were before the plunge in precious metals.

But weakness extended throughout the commodities-related Dow stocks. Oil giants Chevron (CVX 0.44%) and ExxonMobil (XOM 0.02%) are both down more than 1.5% on fears that China's slowdown will cascade throughout the global economy, reducing overall levels of industrial activity and thereby removing key support for the relatively high oil prices that have persisted even through the sluggish economic recovery of the past several years. Meanwhile, Alcoa (AA) has dropped 1.5%, following its typical pattern of tracking China's economic health. Yet in the longer term, if a slowdown further weakens aluminum prices, then it could perhaps break the backs of Chinese aluminum producers that have contributed to the glut of supply on the market.

Outside the Dow, precious-metals investments, including bullion-linked ETFs and shares of gold- and silver-mining stocks, took the biggest hits. The key question investors in precious metals face is whether today's action represents panic-selling from which a longer-term recovery could build or the beginning of a long-term downtrend as the Fed considers potential interest-rate hikes that will increase the opportunity cost of owning gold. Investors need to consider both possibilities as they assess whether now is the right time to buy.