Question 1

Well, technically it is a mineral because a rock is one or more minerals. The way you tell a rock from a mineral is by testing it. If you think it is a mineral, you would look at the color, and test for streak, luster, hardness, cleavage, chemical composition, magnetism, and maybe even taste and smell (only applying to sulfer and halite)! If you were testing for a rock, you would look at grain size and mineral content. With the grain size, you would determine if it was intrusive (large grains) or extrusive (small, almost microscopic grains). Then you would look at the mineral content. If it was lightly colored, you would classify it as felsic but if it had much darker pigments, it would be mafic.

If you ever "stumble" upon a rock and are curious about it, you have two options. The first being you could use basic knowledge of grain size, mineral content and the classification system of minerals (only the ones you could see with your eyes of course) to determine what it is. Your second option would be to take it one step further. If you have the oportunity, you could test it with an acid, test the hardness and streak. If you don't think it is a mineral, you could compare it to other rocks, and use various flow charts to determine what rock you think it is.