There are many ways to determine what minerals are present in a sample. You can observe its color, streak, luster, magnetism, cleavage and hardness. Obviously, you can see what color it is and whether it is metallic or cloudy, but other tests may be required. Streak is tested by rubbing the mineral onto a streak slab of concrete to see what color the powder is. Magnetism is determined by putting a magnet next to the sample, or placing it next to a dish of iron filings. Cleavage is determined by cracking the sample to see the way it fractures. Finally, to determine hardness, you scratch test rocks with the sample, like as controls. I hope this answered your question. (Also, questions like this would best fit under chemistry, because geography is the study of political land)
