by Roberto — Janie's re­cent Bio-Brick post, where she in­tro­duces mi­cro­bi­al­ly in­duced cal­cite pre­ci­pi­ta­tion, prompt­ed me to con­tinue on the to­pic. In con­trast to the amor­phous chalk Janie de­scribed, which is pro­duced by bac­te­ria from lime­stone, I'll be de­scrib­ing a ve­ry dif­ferent sort of chalk. Still cal­cium car­bo­nate, but with a com­ple­te­ly dif­fer­ent ge­ne­sis.