Difference Between Limestone and Chalk l Limestone vs Chalk

The key difference between limestone and chalk is that the limestone contains both minerals, calcite, and aragonite whereas chalk is a form of limestone which contains calcite.

Limestone is a type of sedimentary rock. It mainly contains different crystal forms of calcium carbonate. Therefore this mineral is highly alkaline. Chalk is a form of limestone. It has many favorable properties, which we will discuss below. Although it is a form of limestone, 99% of this mineral contains calcite type crystal form.


1. Overview and Key Difference
2. What is Limestone
3. What is Chalk
4. Side by Side Comparison – Limestone vs Chalk in Tabular Form
5. Summary

What is Limestone?

Limestone is a sedimentary rock, which contains two major types of minerals; calcite and aragonite. These minerals are different crystal forms of calcium carbonate (CaCO3). This sedimentary rock forms as a result of the deposition of skeletal fragments of marine organisms such as coral, forams and molluscs. Therefore, this mineral mostly forms in clear, warm and shallow marine waters. However, this sedimentary rock can form by the precipitation of calcium carbonate from lake or ocean water as well.

The reason why these rocks form in clear, warm and shallow marine waters is that this type of environment allows the marine organisms to form calcium carbonate shells. Moreover, their skeletons can easily extract the necessary ingredients form ocean water. then when these organisms die, their skeletal debris accumulates as sediment. This sediment later lithify into limestone. In addition to that, the waste products of these organisms also contribute to the formation of this sedimentary rock.