Platinum
then comes gold etc but first comes the platinum metal group. but metals that hard to track that's a different scenario but just in case you might be interested metal in the bottom of the periodic table are very rare to get due to the reaction they have with oxygen in the air therefore we can't get hold of them.
but yeah platinum is most expensive and alongside platinum osmium and other few metals as well.
then comes gold etc but first comes the platinum metal group. but metals that hard to track that's a different scenario but just in case you might be interested metal in the bottom of the periodic table are very rare to get due to the reaction they have with oxygen in the air therefore we can't get hold of them.
but yeah platinum is most expensive and alongside platinum osmium and other few metals as well.
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The artificial radioactive ones - ununium etc.