Which of the following is a characteristic of igneous rock?

Step 1: Analyze the question The question asks for a characteristic of igneous rocks, which are rocks formed from the cooling and solidification of molten material (magma or lava).

Step 2: Explain the concept

• Igneous rocks (e.g., granite, basalt, gabbro) form when magma cools. • Intrusive (plutonic) rocks like granite cool slowly underground, forming large, visible crystals. • Extrusive (volcanic) rocks like basalt cool quickly at the surface, forming tiny crystals or glassy textures.
• Because they form from cooling melt, they are typically hard, massive, and crystalline.
• They usually lack layers (bedding) and do not contain fossils.

Step 3: Evaluate each option

• A. Loose in composition ✗. Loose material (sand, gravel) points to unconsolidated sediments, not igneous rock.
• B. Arranged in layers ✗. Layering (stratification or bedding) is a feature of sedimentary rocks.
• C. Crystalline in nature ✓. Igneous rocks are made of interlocking mineral crystals formed as magma cools.
• D. Porous in granular structure ✗. Porous, granular textures are typical of sedimentary rocks like sandstone.

Step 4: Answer The correct option is C. Crystalline in nature.

Exam tip: Use this memory aid:

• Igneous = Crystals (cooled from fire/melt)
• Sedimentary = Strata/layers and fossils
• Metamorphic = Foliation/banding (changed by heat and pressure)

If you see "layers," "fossils," or "porous," think sedimentary. If you see "crystals" or "no fossils," think igneous.