Marble is a metamorphosed -------

Step 1: Analyze the question The question asks which parent rock marble forms from when it is changed (metamorphosed) by heat and pressure.

Step 2: Explain the concept Metamorphic rocks form when existing rocks (igneous, sedimentary, or other metamorphic rocks) are changed by intense heat, pressure, or chemical action, without fully melting. Some common pairs are:

| Parent rock | Metamorphic rock | |---|---| | Limestone | Marble | | Sandstone | Quartzite | | Shale/Clay | Slate, then schist | | Granite | Gneiss | | Coal | Graphite/Anthracite |

Step 3: Work through the options

• A. Basalt: an igneous rock. It changes into greenschist or amphibolite, not marble.
• B. Granite: an igneous rock. It changes into gneiss.
• C. Gabbro: an igneous rock. It changes into amphibolite or similar rocks.
• D. Limestone: a sedimentary rock made mainly of calcium carbonate (CaCO₃). Heat and pressure recrystallize the calcite, which produces marble.

Step 4: Answer Marble is metamorphosed limestone, which is option D.

Exam tip: Remember "Limestone → Marble" (both are L and M, like "Let's Make marble"). Also remember "Sandstone → Quartzite" and "Granite → Gneiss" (both start with G). Learning these pairs can win you quick marks in WASSCE, NECO, and JAMB.