There are more than a few things that can have that general appearance, so images only go so far in aiding identification. Anywhere in the woods in North America, the melted aluminum cans are the most prevalent. And well match what you have provided thus far.
Acid tests are problematic, in my opinion, unless you are well experienced in their use. I have met way too many people who have mistaken brass for gold after testing. Not knocking you, I simply do not know your experience level with testing solutions.
Is it heavy in comparison to an equal size piece of steel, copper, or brass? Or is it light in comparison?
Which area was it found in? I do know platinum can be found in areas of Oregon south of the Rogue and in the general area of the Smith and Klamath in northwest California. Somewhere in the attic is a report of known platinum occurances in California, but I do not feel like looking for it.
Time for more coffee.
