Minerals, Crystals, and Metamorphic Rocks

Topic 1: Mineral and Crystal Formation

Silicates are the most common minerals and crystals. These include:

• Olivine
• Mica (biotite and muscovite)
• Feldspar
• Quartz

Crystals are minerals with a geometric form, flat faces, and vertices. They are ordered solids with an internal structure.

Texture refers to the shape, size, and arrangement of crystals.

Crystal Formation:

• Solidification of molten materials, forming crystals as plutonic rocks cool from magma.
• Sublimation of dissolved substances in gases, creating crystals like sulfur in volcanic conditions.
• Chemical precipitation from an aqueous solution, forming crystals like halite and gypsum. This process requires time, space, and rest.

Metamorphism

Metamorphism alters a rock's mineralogical composition and texture.

Factors influencing metamorphism:

• Temperature
• Pressure (affecting volume and foliation)
• Presence of fluids

Types of Metamorphism:

• Dynamic Metamorphism: Increased pressure, especially at depth, with directed pressure causing faulting and mylonite formation.
• Contact or Thermal Metamorphism: Increased temperature due to igneous intrusions, forming hornfels.
• Regional or Thermodynamic Metamorphism: Increased pressure and temperature in the continental crust, often in subduction zones.

Changes During Metamorphism

• Increased density
• Formation of new minerals
• Recrystallization
• Crystal reorientation

Foliated Textures: Gneiss, slate, and schist.

Non-foliated Textures: Marble and quartzite.

Metamorphic Rocks

Rocks with Foliation:

• Slate (very fine-grained, laminated foliation plane)
• Phyllite (thin, flat foliation, shiny)
• Schist (thick, wavy foliation)
• Gneiss (coarse, less distinct foliation)

Rocks without Foliation:

• Marble (coarse-grained calcite crystals)
• Quartzite (fine or coarse-grained quartz crystals)

Topic 2: Magma

Magma is molten silicate containing significant amounts of gases. It exists within the Earth's crust and parts of the mantle.

Origin of Magma: Rock fusion occurs within a temperature range, a process called anatexia.

Causes of Melting:

• Temperature increase (e.g., friction between tectonic plates)
• Pressure decrease
• Water incorporation

Magma Locations: Destructive plate boundaries, constructive plate boundaries, and intraplate settings.

Cooled magma forms plutonic rocks. Other rocks are volcanic.

Types of Magma:

• Basaltic (partial melting of peridotites in the mantle)
• Andesitic (partial melting of subducted basalt in the crust)
• Granitic (subduction zones, melting of continental crust materials)

Igneous Rock Formations

Magma reaching the crust forms igneous intrusions.

Plutonic Forms:

• Pluton (large intrusive rock mass; a batholith is a very large pluton)
• Laccolith (lens-shaped intrusion with a flat base and domed roof)
• Sill (tabular intrusion parallel to host rock structures)
• Dike (short tabular intrusion across host rock structures)

Volcanic Forms:

• Volcanic Chimney (circular conduit for magma flow)
• Cone (a volcano formed by accumulating magmatic materials around a crater; a stratovolcano is formed by layers of lava and pyroclastic material)
• Caldera (large circular depression formed by volcanic collapse)