As a dyer I depend on sodium carbonate to activate the Procion dyes I use. And as I looked through my photo collection today it was easy to see how dependent I am on the inspiration of limestone -- calcium carbonate. My chemist father would be proud of me for noticing the familial similarity.
"Sodium carbonate (also known as washing soda or soda ash), Na2CO3, is a sodium salt of carbonic acid. It most commonly occurs as a crystaline heptahydrate which readily effloresces to form a white powder, the monohydrate. It has a cooling alkaline taste, and can be extracted from the ashes of many plants. It is produced artificially in large quantities from common salt." (from Wikipedia)
"Calcium carbonate is a chemical compound, with chemical formula CaCO3. It is commonly used medicinally as a calcium supplement or as an antacid. Calcium carbonate is the active ingredient in agricultural lime. It is a common substance found as rock in all parts of the world and is the main component of seashells and the shell of snails. It is usually the principle cause of hard water." (from Wikipedia)
Here are some examples of the latter:
If you have a great photo of limestone in nature or limestone in architecture, send it to me at email@example.com and I will include it and a credit for your photo in a followup post.