Help identifying rock?
Looks like massive (as in the individual crystals have grown into each other) Quartz, the different colours are due to minerals either dissolved into the crystal structure, those are the dark areas, or simply staining the surface as with the rusty red/orange sections. It could be Calcite or Salt, the first will react with Vinegar and second will dissolved in hot water but both are rather fragile and it would be easy to break off small samples.