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Having gone to the trouble of measuring the Specific Gravity, did you not then go on to look up the SG values for various metals? They’re easy enough to find on the net.
Obviously, if it’s an alloy, a whole host of materials could be in the region of 7.5 but, as pure metals, the maximum SGs for silver and platinum are way above the value you quote and aluminium is way below it:
Platinum: 21.5
Silver: 10.6
Aluminium: 2.8
Tin, as pure metal, would have an SG of 7.5 but of course that’s not the only possibility if your lump of something is one of the denser metals alloyed with others of lower density.