They all appear to be micro-crystalline in structure for the most part. The black one looks to be water worn Obsidian or volcanic glass. The lower right and upper left stones in the left photo looks like they could be Dolomite or Tourmaline they are both micro-crystalline forms of chert or flint and should show what look like layers similar to a jawbreaker candy if you break it. It is hard to tell from the photo, but the lower left stone appears to be similar or possibly an untarnished chalcopyrite based on the color. The first three I described were used by ancient peoples for making arrowheads, spear tips, knives and scrapers and are still worked by hobbyist in the same fashion as they were throughout history. The last is usually yellow in color and is a sulfide of copper and iron and a main ore of copper. If you had higher resolution photos from different angles and a general description of the location where they were found, I could possibly be more precise in the identification as it helps to narrow the Geology of the area. Hope this helps
-Keith
