Shiny stuff could be mica. Could also be trace metals. Start with a magnet. Except for precious metals most metals are magnetic. Metal is very heavy for its size. The difference between metal and rock is pronounced. A fist sized piece of metal would seem like a cannonball. A rock the same size would be heavy but not even in the ball park. You could try scraping some off, weighing the material, burning away impurities and then testing the remaining metal by weighing it and seeing how much water it displaces and doing the math to get a weight to volume measurement and compare that ratio to ratios of known metals. We did that in pysical science. Be sure to use all safety precautions like gloves, safety glasses and do this in a properly vented area.. start with the magnet and proceed carefully. Let us know what you find.