2 ounce blocks of super-pure, bone-dry chalk. Box of 8. CAMP chalk (a form of magnesium carbonate (4MgCO3-Mg(OH)2-4H2O) is tested by an independent laboratory to verify its purity. The measured content of silicon is just 0.021% (equivalent to 0.043% crystalline silica), far less than the dangerous threshold and far ahead of the industry standard. Most climbers do not realize that simple climbing chalk can actually contain numerous impurities and additives. Recent studies have shown that inhaled chalk dust is harmful to the lungs if it contains more than 1% crystalline silica. Drying agents have also been known to contribute to cracking of the skin and decreased friction.