It's pointy and non-soluble. You breath in little microscopic needles of Asbestos dust, they stick in your lungs, damage cells, irritate tissues, etc.
Your body can't remove the pieces.
They keep causing damage, and cells under such stress of repeated damage, replacement, damage, replacement, irritation, scarring, damage, replacement, are more likely to develop tumours.
It causes inflammation in your lungs. Inflammation leads to death of cells, and thise need to be replaced by the remaining cells dividing, thus forming new ones. Every time a a cell replicates, mutations, aka changes in DNA happen. While most of them are harmless, some occur in just the right places to cause deregulation of cell growth and proliferation. Tumors/cancer formed.