The other day, I went to a local library to look at the CRC Handbook. I was trying to find out about the solubility of silicon dioxide. Anyway, I noticed that sodium chloride was listed as "colorless". This struck me as odd. I had always considered it as white. The table seemed to differentiate between white and colorless. It listed sodium carbonate as white, yet sodium chloride as colorless. So, my question is: What is "colorless"? I agree that Na2CO3 is white, but all the crystals if NaCl I have ever seen... I would not describe them as clear or colorless. Silicon dioxide is also listed as colorless. However, large crystals of it appear much more transparent than those of sodium chloride.