Which is/are correctly matched ?
Original Igneous/ Sedimentary Rock → Metamorphic Rock
(i) Limestone → Marble
(ii) Gabro → Serpentine
(iii) Mica → Schist
(iv) Sandstone → Gneiss

Question

Which is/are correctly matched ? 
Original Igneous/ Sedimentary Rock → Metamorphic Rock 
(i) Limestone → Marble 
(ii) Gabro → Serpentine 
(iii) Mica → Schist 
(iv) Sandstone → Gneiss

Accepted Answer

Here's a detailed explanation justifying why Option 1 is the correct answer and why the other options are incorrect, based on the provided information:

**Why Option 1 is Correct: (i), (ii) and (iii)**

*   **(i) Limestone → Marble:** This is a correct match. Limestone, a sedimentary rock primarily composed of calcium carbonate (CaCO3), undergoes metamorphism (typically due to heat and pressure) to form marble. The calcium carbonate recrystallizes, resulting in a harder, denser rock with a characteristic crystalline texture.

*   **(ii) Gabro → Serpentine:** This is also a correct match. Gabbro, a mafic igneous rock, can undergo hydrothermal metamorphism (alteration by hot, chemically active fluids). This process, often called serpentinization, transforms the minerals in gabbro (like olivine and pyroxene) into serpentine minerals.

*   **(iii) Mica → Schist:** This is a correct match. Mica is a common mineral found in many igneous and sedimentary rocks. Under metamorphic conditions (heat and pressure), mica minerals align and grow, contributing to the foliated texture characteristic of schist. Schist is a metamorphic rock defined by its prominent foliation (parallel alignment of platy minerals like mica).

**Why the Other Options are Incorrect:**

*   **Option 2: (i), (ii) and (iv)** This option includes (i) and (ii) which are correct, but it also includes (iv) Sandstone → Gneiss, which is incorrect.

*   **Option 3: (ii), (iii) and (iv)** This option includes (ii) and (iii) which are correct, but it also includes (iv) Sandstone → Gneiss, which is incorrect.

*   **Option 4: (i), (ii), (iii) and (iv)** This option includes all four transformations, but (iv) Sandstone → Gneiss is incorrect.

**Why (iv) Sandstone → Gneiss is Incorrect:**

*   **(iv) Sandstone → Gneiss:** This is an incorrect match. While sandstone *can* undergo metamorphism, it typically transforms into quartzite. Gneiss is a high-grade metamorphic rock characterized by distinct banding (layers of different mineral compositions). Gneiss usually forms from the metamorphism of either sedimentary rocks like shale or igneous rocks like granite. Sandstone (primarily composed of quartz) will become quartzite, a hard, non-foliated metamorphic rock. While under extreme conditions, a sandstone with significant clay content *could* contribute to the formation of a gneissic rock, it's not the direct and typical transformation. The more common and direct metamorphic product of sandstone is quartzite.

In summary, only (i), (ii), and (iii) represent correct transformations of original rocks into metamorphic rocks. Therefore, Option 1 is the only correct answer.