Which of the following pairs of rock examples are sedimentary rocks?

Step 1: Analyze the question You are asked to find the pair in which both rocks are sedimentary.

Step 2: The concept Rocks fall into three main groups:

• Igneous: formed from cooled magma or lava (e.g., granite, gabbro, basalt).
• Sedimentary: formed from the compaction and cementation of sediments, or from organic or chemical deposits (e.g., sandstone, limestone, chalk, shale, coal).
• Metamorphic: formed when existing rocks are changed by heat and pressure (e.g., schist, gneiss, slate, marble, graphite).

Step 3: Check each option

• A. Graphite and sandstone: Sandstone is sedimentary, but graphite is metamorphic. ✗
• B. Gabbro and schist: Gabbro is igneous and schist is metamorphic. ✗
• C. Limestone and chalk: Both are sedimentary. Limestone forms from calcium carbonate deposits and shell remains, and chalk is a fine-grained form of limestone made from microscopic marine organisms. ✓
• D. Gneiss and granite: Gneiss is metamorphic and granite is igneous. ✗

Step 4: Answer The correct option is C. limestone and chalk.

Tip: Remember that sedimentary rocks are often layered (stratified) and may contain fossils. Rocks made of calcium carbonate, such as limestone and chalk, are sedimentary. For metamorphic rocks, think of the "banded or foliated" ones like gneiss and schist.