Geologically, marble is known as
🪨 Understanding Geological Classification
The geological classification of rocks is based on their origin, or how they were formed. This question asks you to identify the formation process of marble.
🔬 Detailed Analysis of the Options
C. Metamorphic Rock
This is the correct answer. Marble is a classic example of a non-foliated (unbanded) metamorphic rock. It is not a primary rock but is formed when a pre-existing rock is subjected to intense heat and pressure, causing its structure to change.
- Parent Rock: Marble is formed from the metamorphism of Limestone (or sometimes Dolostone), which are sedimentary rocks.
- Formation Process: When limestone is buried and exposed to the high temperatures and pressures of metamorphism, the original calcite crystals in the limestone recrystallize to form a denser rock with larger, interlocking crystals. This process destroys the original layers and fossils that may have been present in the limestone.
A. Sedimentary Rock
This is incorrect. While marble's parent rock (limestone) is sedimentary, marble itself has been fundamentally changed by heat and pressure, placing it in the metamorphic category.
B. Igneous Rock
This is incorrect. Igneous rocks are formed from the cooling of magma. Marble is formed from the alteration of a solid sedimentary rock.
D. Stratified Rock
This is a structural classification, not a geological one. "Stratified" simply means the rock is formed in layers (strata). While limestone is often stratified, the process of metamorphism that creates marble typically erases these layers as the crystals recrystallize, making marble a non-stratified (or non-foliated) rock.
➡️ From Limestone to Marble: The Transformation
| Property | Limestone (Parent Rock) | Marble (Metamorphic Rock) |
|---|---|---|
| Rock Type | Sedimentary | Metamorphic |
| Composition | Mainly Calcite | Recrystallized Calcite |
| Texture | Often contains fossils and visible layers | Interlocking crystals, sugary texture |
| Hardness | Relatively soft | Harder and denser than limestone |
💡 Study Tips
- "M" for Marble, "M" for Metamorphic: This is an easy way to connect the rock to its geological class.
- Think of a Statue: Famous statues are carved from marble. The beautiful, crystalline stone used for art is a result of the intense heat and pressure of metamorphism.
- Remember the Parent: The transformation of Limestone → Marble is one of the most important examples in geology, just like Sandstone → Quartzite.