Question

select the correct answer.

which of these igneous rocks is intrusive?

granite
obsidian
both granite and obsidian
neither granite nor obsidian

Explanation:

Define intrusive and extrusive igneous rocks

Igneous rocks form from cooling magma or lava. Intrusive igneous rocks cool slowly beneath Earth's surface, allowing large, visible mineral crystals to grow. Extrusive igneous rocks cool rapidly on or near the surface, resulting in a fine-grained or glassy texture with tiny or no visible crystals.

Analyze the properties of obsidian

Obsidian is volcanic glass that forms when lava cools extremely rapidly on Earth's surface. Because it cools almost instantly, no mineral crystals have time to grow, giving it a smooth, glassy texture. This makes obsidian an extrusive igneous rock.

Analyze the properties of granite

Granite forms when magma cools slowly deep underground. This slow cooling process gives mineral crystals ample time to grow, resulting in a coarse-grained texture with clearly visible, interlocking mineral grains (such as quartz, feldspar, and mica). This makes granite an intrusive igneous rock.

Identify the correct option

Comparing the two rocks, granite is the intrusive igneous rock, while obsidian is extrusive. Therefore, the correct choice is granite.

Answer:

• granite (Correct answer)
• obsidian
• both granite and obsidian
• neither granite nor obsidian