Which of the following examples of igneous rock is extrusive?

Step 1: Analyze the question You are asked to pick the igneous rock that is extrusive.

Step 2: Explain the concept Igneous rocks form when magma or lava cools and solidifies. There are two main types:

• Intrusive (plutonic) rocks: Magma cools slowly underground. The slow cooling gives large, visible crystals (coarse-grained texture). Examples are granite, gabbro, diorite and dolerite.
• Extrusive (volcanic) rocks: Lava cools quickly on the Earth's surface. The fast cooling gives tiny crystals (fine-grained or glassy texture). Examples are basalt, rhyolite, andesite, obsidian and pumice.

Step 3: Check each option

• A. Granite: Intrusive, coarse-grained, with large crystals formed deep underground.
• B. Basalt: Extrusive, fine-grained, formed from lava cooling at the surface. The Deccan Traps in India are a famous example of basalt flows.
• C. Gabbro: Intrusive. It has the same composition as basalt but cooled slowly underground, so it is coarse-grained.
• D. Diorite: Intrusive, coarse-grained. Its extrusive equivalent is andesite.

Step 4: Answer Only basalt forms from lava at the surface, so the correct option is B. Basalt.

Tip: Remember that extrusive rocks "exit" the volcano. Common extrusive rocks include Basalt, Rhyolite and Andesite. Many students use the pairing "Basalt ↔ Gabbro" (extrusive ↔ intrusive) to avoid mixing them up. Other pairs are Rhyolite ↔ Granite and Andesite ↔ Diorite.