Primary rocks, also known as igneous rocks, are formed directly from the cooling and solidification of magma or lava. They can be classified into three main categories based on their texture and mineral composition:

1. Intrusive Igneous Rocks:

• Formed when magma cools beneath the Earth’s surface, resulting in coarse-grained textures.
• Examples:
  • Granite: a common type of intrusive igneous rock with a coarse-grained texture and a mixture of quartz, feldspar, and mica minerals.
  • Gabbro: a dark-colored, coarse-grained rock with a high iron and magnesium content.

2. Extrusive Igneous Rocks:

• Formed when lava cools and solidifies above the Earth’s surface, resulting in fine-grained textures.
• Examples:
  • Basalt: a dark-colored, fine-grained rock with a high iron and magnesium content.
  • Andesite: a medium-colored, fine-grained rock with a mixture of quartz, feldspar, and pyroxene minerals.

3. Volcanic Glass (Obsidian):

• A type of extrusive igneous rock that forms when lava cools rapidly, resulting in a glassy texture.
• Characteristics:
  • Vitreous luster
  • Conchoidal fracture
  • Often black or dark brown in color

Other Types of Primary Rocks:

• Kimberlite: an ultramafic intrusive rock that forms from magma rich in magnesium and chromium.
• Komatiite: an ultramafic extrusive rock that forms from highly viscous lava.
• Pumice: a light-colored, porous volcanic rock that forms when lava is ejected into the air and rapidly cools.