Below, we outline 20 of our favorite quotes about the hard-asset industry with which all investors should be familiar.

• “Commodities tend to zig when the equity markets zag.” – Jim Rogers

• “When interest rates are low we have conditions for asset bubbles to develop, and they are developing at the moment. The ultimate asset bubble is gold.” – George Soros

• “Gold gets dug out of the ground in Africa, or someplace. Then we melt it down, dig another hole, bury it again and pay people to stand around guarding it. It has no utility. Anyone watching from Mars would be scratching their head.” – Warren Buffett

• “There is enough oil out there for world demand. It is true that a lot of what’s driving oil prices up right now is not the lack of supply. There’s enough supply." – President Barack Obama

• “Historically, there has been a bull market in commodities every 20 or 30 years.” – Jim Rogers

• “The problem with commodities is that you are betting on what someone else would pay for them in six months. The commodity itself isn’t going to do anything for you…it is an entirely different game to buy a lump of something and hope that somebody else pays you more for that lump two years from now than it is to buy something that you expect to produce income for you over time.” – Warren Buffett

• “ Gold is not overvalued at $500, and gold will not be overvalued at $1,500 or $2,000. The real money is buying gold and putting it away.” – Peter Schiff

• “What motivates most gold purchasers is their belief that the ranks of the fearful will grow…As ‘bandwagon’ investors join any party, they create their own truth — for a while.” – Warren Buffett

• “When you look at a commodities market you need hedgers and speculators. If you don’t have one, you don’t have a market. That’s how it works.” – T. Boone Pickens

• “Fifty-dollar oil is just another stop on the road to much higher crude prices.” – Peter Schiff

• “All those commodities are going to have to rise in value as we are in short supply and we are printing too much money." – Peter Schiff

• “The price of a commodity will never go to zero. When you invest in commodities futures, you’re not buying a piece of paper that says you own an intangible piece of company that can go bankrupt.” – Jim Rogers

• “Soaring prices for crude oil, falling production surpluses, wild speculation in commodities, a rush into the precious metals, turmoil in the Middle East, assertive oil producers: it is 1973-74 all over again, and at dictation speed.” – James Buchan

• “The exchangeable value of all commodities rises as the difficulties of their production increase.” – David Ricardo

• “The strength in gold is revealing the general weakness in the dollar.” – Peter Schiff

• “Shale gas has provided the United States the opportunity to have 100 years of supply that is domestically produced. If we are going to develop natural gas from shale, it has to be done in a safe and responsible manner.” – Ken Salazar

• “Natural gas is a better transportation fuel than gasoline, so if that’s the case, it’s cheaper, it’s cleaner and it’s a domestic resource.” – T. Boone Pickens

• “Like other commodities, gold and silver have an intrinsic value, which is not arbitrary, but is dependent on their scarcity, the quantity of labor bestowed in procuring them, and the value of the capital employed in the mines which produce them.” – David Ricardo

• “The crude oil market, unlike every other commodity in America, is virtually unregulated.” – Peter DeFazio

• “Our culture runs on coffee and gasoline, the first often tasting like the second.” – Edward Abbey

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Disclosure: No positions at time of writing.