While Becca is correct about lightly dusting crickets for supplementation, white salt like crust around the nostrils is generally not calcium and is more apt to be potassium chloride, sodium chloride or may simply be sodium or potassium. Many lizards (not all) have salt glands which aid them in maintaing homeostasis through secretion of excess salts. This can be seen as a dry, white substance in or around the nostrils, if excessive it can be gently swabbed off with a warm, moist Q-Tip. If the excreted substance has the consistency of mucus, that's an entirely different issue. If you need help it is always beneficial to fill out the "How to ask for help" thread in the "Health Clinic" section of this forum. That way any husbandry issues can be identified if the problem is associated with that. Pics are a plus too! Hope this helps!