spider chalk manufactures pure, lab-grade magnesium carbonate block chalk in 5.5 oz (150 grams) mega blocks. mega blocks last 2x longer than conventional blocks 1 lb spider chalk = 2 lbs of regular blocks. we are the only manufacturer of gym and weightlifting chalk in the usa. May 19, 2018 · gym chalk block2oz magnesium carbonate, pigment free, non-toxic chalk block keeps hands dry, prevents blisters and calluses while reducing slippage during your workout improves grip and handle: great for gymnastics, rock climbing, bouldering, and all power and weight lifting activities including deadlifts, pull-ups, kettlebells and more The gym chalk applies easily, holds its form on the block, and doesn’t crumble or turn to powder as much as others. made with 100% pure magnesium carbonate, urban strength’s ultimate grip gym chalk is the go to product for weightlifters, cross-fitters, ninja warriors, climbers, and gymnastic athletes alike. Here is an easy homemade liquid chalk recipe along with the benefits of using it. what is gym chalk. magnesium carbonate, a white mineral, is known as gym chalk or climbing chalk, due to its use in activities like weightlifting, rock climbing, athletics, and gymnastics.