The value of a rock specimen can vary, depending on the minerals it is comprised of as well as its appearance. To establish the monetary value of a rock test it for color, clarity, hardness, and surface markings. Size plays a factor in worth as well; Bigger is better! Scarcity is another factor that can play a role into a rock's worth. Value of a rock can also depends on where it falls on the Mohs scale (1 to 10 regarding hardness). The harder a rock, the more valuable.