Laterite Identification: Non-Calcareous Rocks

The question asks to identify the rock type that does not contain calcium carbonate, meaning it is not calcareous. Calcareous rocks are primarily composed of or contain significant amounts of calcium carbonate (CaCO₃).

Understanding Calcareous Rocks

Calcareous rocks are defined by their composition. Let's examine the options provided:

• Limestone: This is a common sedimentary rock that is primarily composed of calcium carbonate, often in the form of the mineral calcite. It is inherently calcareous.
• Marl: Marl is a calcium-rich, earthy material composed of varying amounts of clay and calcium carbonate. It is considered calcareous due to its calcium carbonate content.
• Chalk: Chalk is a specific type of limestone, known for its softness and white color. It is composed of calcite, a form of calcium carbonate (CaCO₃). Therefore, chalk is calcareous.
• Laterite: Laterite is a soil and rock type that forms in hot, wet tropical and subtropical regions. It is typically rich in iron and aluminum oxides and hydroxides, such as goethite, gibbsite, and hematite. Laterite is characterized by its high concentration of these minerals and typically lacks significant amounts of calcium carbonate.

Conclusion on Laterite

Based on the composition of each rock type, laterite stands out as the rock that is not calcareous. Its formation process and mineral composition are distinct from limestone, marl, and chalk, which are all defined by their calcium carbonate content.