Let's start with a few facts.
There are no natural 28 lb platinum nuggets - ever. The largest platinum nugget found in the U.S. was 1/2 ounce.
Hawaii has no platinum nuggets. Wrong geology.
Your pictures and information don't give us any idea of size or shape. You haven't given us any idea of how you came about this rock or where it's from. You have performed no tests that might give us a clue what we are commenting on.
Here's a video by my friend Chis that helps explain platinum occurrences and how to identify platinum.
In short it's not platinum and you haven't provided enough information for anyone to actually help you determine what it is.
Maybe start over with sharp pictures taken in daylight of the whole object with a scale in the picture. Then move on to streak, hardness and specific gravity tests. Share with us what part of the planet you found this rock on.
Playing charades is no way to determine the composition of a rock. We need actual information about the rock itself, not what you hope it is.