Limestone, marble and chalk are all forms of Calcium Carbonate. The difference lies in the formation of these rocks: Chalk is a compaction of tiny fossil seashells, marble is a metamorphic rock and limestone a sedimentary rock. Blackboard-chalk is really compressed gypsum, Calcium Sulphate. read more
Limestone, marble and chalk are all forms of Calcium Carbonate. The difference lies in the formation of these rocks: Chalk is a compaction of tiny fossil seashells, marble is a metamorphic rock and limestone a sedimentary rock Blackboard-chalk is really compressed gypsum, Calcium Sulphate. read more
"Chalk" is a variety of "limestone" which is composed primarily of the shells of single-celled, calcium carbonate secreting creatures. Think about this next time you use chalk - that white stuff all over your hands is actually countless individual shells, each microscopic in size and the former home of a living being. read more
« Reply #4 on: 15/12/2013 09:45:25 » Chalk is formed in a deep marine environment from the shells of microscopic algae which flourish near the surface, but die and fall to the seafloor. read more