How to distinguish different crystals

Hi, During the process of protein crystallization many salts are present in the buffer we use…now when these salts can also form crystal, how do we know which is a protein crystal and which one is a salt crystal (prior to x-ray diffraction study)?

Leemark

Two simple tests could be done for this

  1. Protein crystals typically have well-defined, characteristic shapes (e.g., cubes, rods, needles, or plate-like structures) that are more uniform and often reflect light in a particular way due to their internal structure. Protein crystals are usually more transparent and may be larger, though not always. On the other hand, Salt crystals tend to have a more regular geometric shape, such as cubes or rhombohedra, and can be much smaller than protein crystals and are usually opaque.
  2. Salt crystals are often more numerous and may cluster together more than protein crystals.