Environmental Science Minerals of the Environment Physical Properties of Minerals Mineral are identified by their physical characteristics. Luster refers to the way that light reflects off of surfaces of the mineral. To see the later, mineralogists will scratch a sample on a porcelain streak plate and look at the color of its streak. When we talk about color, we should describe both the color of a bulk mineral and the color of its streak. Hardness refers to the ability of one material to scratch another.
Cleavage refers to the way that a mineral breaks.
Minerals with cleavage will tend to break along parallel planes. Weathered surfaces may be chalky looking due to alteration to clay. In general the different clay minerals can be distinguished ONLY by X-ray diffraction. Massive serpentine has a hardness of approximately 4. Carbonates have 3 non-orthogonal cleavages which produce rhombic shaped cleavage fragments.