When the Washington Monument was built, aluminum was very difficult to extract and thus among the most expensive metals.
Now you know why the Washington Monument is capped with aluminum.
Because efficient extraction of aluminum from bauxite ores is done with hydroelectric power, which was not available when the Washington Monument was built. Ironically, the center of US aluminum production through Wold War Two was up here in the Pacific Northwest, because the public works projects of the late 1930s built a bunch of hydroelectric dams along the Columbia River, and we still get a high percentage of our electricity from them - it made aluminum production both cheap and easy up here.
@Krajzen, you are preaching to the choir! Most of the 'strategic resources' in the game are limited because of the technology and industrial infrastructure required, not the ores or raw materials (as in the hydroelectric example for aluminum in the previous paragraph).
Iron is another good example: abundantly available, at least in the relatively small quantities required for pre-industrial use. The limiting factor was technology: forced-air draft furnaces to reach high enough temperature to produce 'wrought' iron, the even higher temps required to melt the iron and produce cast iron, and the techniques of adding just the right amount of carbon and removing the 'extraneous' impurities to produce Steel, and finally adding the right alloy materials to produce armor plate and specialized steel alloys for modern construction. Obtaining the iron ore only becomes a major problem and limiting factor when you need it in quantities of 1000s of tons - as in, when you are trying to build railroads, battleships and cities full of skyscrapers, or the Industrial Era and later.
Oil, unfortunately, is the Outlier. For the bulk of the post-industrial eras, there is simply no substitute for it to run everything military, and the requirements, as for modern steel, are in the 1000s of tons and it tends to be readily available only in certain areas which, therefore, become instantly of Major Strategic Importance. The historical fact is that countries without lots of oil got hammered by those who had it, and cutting the supply of oil was the quickest way to strangle any enemy military forces - see Germany and Japan in World War Two for the most obvious examples, but Italy is an even better example: Fascist Italy had a very good navy, but had Zero sources for oil and had to get everything from Germany (who controlled the major European source, the Rumanian Ploesti oil complex). When the Nazis couldn't supply the oil (after 1941) the Italian Navy was Out of the War - they literally couldn't move out of port.
On the one hand, this is a guaranteed Frustration Factor to the player who has laboriously tended his Civ from 4000 BCE to the twentieth century and then discovered he is Oil-less, on the other hand it means, like Italy, that you should only go to war if you have Allies that can give/sell/loan you oil. I personally don't mind having 'extra' strategic/diplomatic decisions to make, but I'm probably in the minority here.