Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: chris on 12/12/2013 09:34:35

Title: What is the difference between chalk, limestone and marble?
Post by: chris on 12/12/2013 09:34:35

Chalk, limestone and marble are all examples of calcium carbonate aren't they? So what is the distinction between them?

Title: Re: What is the difference between chalk, limestone and marble?
Post by: RD on 12/12/2013 11:16:40

Polymorphism (http://en.wikipedia.org/wiki/Crystal_structure#Polymorphism) ?

Title: Re: What is the difference between chalk, limestone and marble?
Post by: Bored chemist on 12/12/2013 13:12:54

I don't think so.
Calcium carbonate does have (at least) two crystal forms (aragonite and calcite), but I think limestone, chalk and marble are all calcite.
I think the difference is due to particle size, how well formed the crystals are and what impurities are present.

Title: Re: What is the difference between chalk, limestone and marble?
Post by: chiralSPO on 13/12/2013 03:39:28

Marble has much larger crystals than either of the other minerals.

Title: Re: What is the difference between chalk, limestone and marble?
Post by: evan_au on 15/12/2013 09:45:25

Chalk  (http://en.wikipedia.org/wiki/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. The kind of chalk used in old-style classrooms and lecture theatres scrapes off a thin layer of fine white dust as they are scraped over the abrasive surface of a "blackboard".

Limestone  (http://en.wikipedia.org/wiki/Limestone#Description)is formed in a shallower marine environment from the bodies of corals and shells, as well as the shells of microscopic sea life. Since it contains large lumps, it does not form such a fine white powder as chalk. 

Marble (http://en.wikipedia.org/wiki/Marble#Physical_origins) is metamorphosed limestone, ie subjected to heat and pressure, the crystals grow and interlock, forming a stronger rock, more suitable for a building material. Sometimes minerals in the original limestone are still visible as swirls of colour in the marble 

They all contain Calcium carbonate. This is mined as one of the ingredients in cement.

Title: Re: What is the difference between chalk, limestone and marble?
Post by: chris on 23/12/2013 09:51:41

Thank you all. Wonderful answers. Chris