Rock types - SS1 Geography Lesson Note

1. Igneous Rocks:

• Structure: Igneous rocks are formed from the solidification of molten material called magma. They can have two primary types of structures:

 

• Intrusive (Plutonic): These rocks form beneath the Earth's surface and cool slowly. As a result, they have larger crystals. Common examples include granite.

 

• Extrusive (Volcanic): These rocks form on the Earth's surface and cool rapidly, resulting in smaller crystals or a glassy texture. Common examples include basalt and pumice.

 

• Color: Igneous rocks can vary in color, but they often appear in shades of black, gray, red, or brown.

 

• Texture: The texture can be glassy (smooth and shiny, in the case of obsidian), coarse-grained (visible crystals), or fine-grained (small or microscopic crystals).

 

2. Sedimentary Rocks:

• Structure: Sedimentary rocks are formed from the accumulation and compaction of sediments, which can include minerals, organic material, or even fragments of other rocks. They often have distinct layers.

 

• Color: Sedimentary rocks come in a wide range of colors, depending on their composition. For instance, sandstone is typically tan or red, while limestone can be white or gray.

 

• Texture: Sedimentary rocks can have various textures, including clastic (particles cemented together), chemical (precipitated minerals), or organic (formed from organic remains). Some may have a smooth, rounded appearance, while others can be rough.

 

3. Metamorphic Rocks:

• Structure: Metamorphic rocks are created from the alteration of existing rocks (igneous, sedimentary, or other metamorphic rocks) due to high pressure and temperature deep within the Earth.

 

• Color: The color of metamorphic rocks can vary widely. For example, marble, which is a metamorphic rock, is often white or gray.

 

• Texture: Metamorphic rocks can have foliated or non-foliated textures. Foliated rocks have a layered or banded appearance, with minerals aligned, like in slate or schist. Non-foliated rocks have a more uniform, granular texture, such as marble.