I have compiled a list of sources for the elements that are available to the amateur chemist. Platinum will be discussed here.
Platinum is a dense, shiny, expensive metal. It is extremely malleable, just like gold, allowing it to be shaped easily. Platinum is quite corrosion resistant as well, making it very useful in chemistry. It only dissolves in aqua regia, not in any other acid. It is attacked by halogens and molten salts though when heated. Platinum forms divalent and tetravalent compounds, both of which are oxidizing and colorful. Platinum sponge is a finely divided form of platinum that is used as a catalyst. It is created by the heating of ammonium platinum(IV) chloride. Platinum is not affected by oxygen at any temperature, making it useful for high temperature work. Platinum was found in ores brought to Spain from the New World. It is often found along with similar precious metals: osmium, iridium, ruthenium, rhodium, and palladium.
In element form: Platinum spark plugs and platinum jewelry are relatively common. Some platinum spark plugs have a center wire of pure platinum, while others have a wide platinum-plated electrode.
In compound form: No sources found.
Here is my sample of platinum. It is a couple of spark plugs. The left has a platinum wire, the right has a platinum-iridium alloy plating on the center electrode.