Types of Rocks Classification

Types of Rocks

• Rocks are classified into three main categories: igneous, sedimentary, and metamorphic.
• Learning competency includes identifying and classifying these rock types.

Igneous Rocks

• Derived from the Latin word "ignis," meaning fire; formed through the solidification of magma or lava.
• Requires high temperatures (not lower than 700°C) to form.
• Common minerals in igneous rocks include quartz, feldspar, pyroxene, olivine, amphibole, and mica.

Formation of Igneous Rock

• Characterized by an intergrowth of crystals and/or volcanic glass.
• Crystal size is proportional to the cooling rate of magma: larger crystals form at greater depths, while smaller ones form near the surface.

Types of Igneous Rocks

• Extrusive Igneous Rocks: Formed from magma or volcanic fragments that erupt and solidify on the surface; typically fine-grained with tiny, indistinct crystals.
• Intrusive Igneous Rocks: Form when magma crystallizes within the Earth's crust, exhibiting medium to coarse grains; also known as plutonic rocks.

Naming of Igneous Rocks

• Naming uses a binary system based on texture and composition (silica content).
• Common classifications include:
  • Felsic: Rhyolite (extrusive), Granite (intrusive)
  • Intermediate: Andesite (extrusive), Diorite (intrusive)
  • Mafic: Basalt (extrusive), Gabbro (intrusive)

Sedimentary Rocks

• Formed from organic, mechanical, or chemical sediments through a process called lithification.
• Example: Coquina, made from seashells or coral.

Formation of Sedimentary Rock

• Diagenesis includes processes where sediments become lithified. The four main steps are:
  • Compaction
  • Cementation
  • Recrystallization
  • Chemical changes (e.g., oxidation/reduction)

Types of Sedimentary Rock

• Non-clastic Sedimentary Rocks: Can be biological, chemical, or a combination of both.
• Key examples include:
  • Chert and Flint (light and dark color variations, respectively) - very fine crystalline texture.
  • Rock Gypsum: Fine to coarse crystalline.
  • Rock Salt: Fine to coarse crystalline.
  • Bituminous Coal: Organic matter derived from altered plant fragments, fine-grained.