Cramer finished his weeklong series on 2010’s top investing themes with a focus on gold. The precious metal shot up 24% last year, marking the ninth straight year where the price increased.

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“And I don’t think gold is done,” Cramer said.

Gold historically has been considered a defensive play. Investors buy it to protect against both inflation and overall market volatility. The idea is that while some stocks in a portfolio are dropping, gold heads the other way, thereby helping to stem big losses. But the commodity has been rallying right along with stocks, turning it into an offensive play as well.

That’s because gold has developed into a legitimate growth investment. As more and more people flood in – net investment in gold jumped fivefold in 2008 – the price increases. A big driver has been investors’ seeking safety as world governments issue billions in cash to fund their economic stimulus programs, and, as a result, debase their currencies.

Many developing nations have used the same strategy, buying gold to maintain their exchange rates because they no longer trust devalued dollars and euros. The central banks of Russia, India and China all have upped their gold holdings over recent years.

Another relevant gold trend concerning the BRIC nations involves their growing middle classes. What do people do with their newly found disposable income? They spend it, of course. And a healthy chunk is going toward gold jewelry.

“Central banks, currencies, interest rates – this stuff is all important,” Cramer said. “But don’t underestimate the power of bling.”

A last couple of points regarding gold: The economy eventually will rebound, meaning inflation is on its way. And again gold is a play on that. So expect the price to rise accordingly. Also, gold producers have reduced their hedges, which is a sign that they too think prices are going higher. Not to mention, they can’t find enough gold to meet the growing demand, and that will play a part here as well.

Cramer does like some gold stocks – and he highlighted those during Friday’s Mad Money – but he said buying bullion is the best bet. Of course, investors can’t safely store gold bars unless they’re willing to pay a depository bank to do the job. So an exchange-traded fund that owns gold and moves in tandem with the commodity’s price is the better play. His favorite is the SPDR Gold Shares ETF [GLD 112.85 1.48 (+1.33%) ] .

The bottom line here is that every portfolio should contain some gold. It plays on both sides of the ball: defensively it protects against market trouble, and offensively it capitalizes on the commodity’s growth.

“Consider it term life insurance for your nest egg,” Cramer said.