Silicate Minerals and Earth's Crust

Silicate Minerals

• Silicate minerals make up about 90% of Earth's crust, composed of oxygen (47%) and silicon (30%) combined.
• Silicate minerals are the largest class of rock-forming minerals.
• Examples of silicate minerals include quartz, feldspar, mica, and pyroxene.

Formation of Silicate Minerals

• Crystals form when molten magma cools, either within Earth's crust or as lava above Earth's crust.
• The size and type of minerals formed depend on the ingredients in the magma and the rate at which the magma cools.
• Magma with low amounts of silica produces darker colored minerals, while magma rich in silica produces lighter minerals.

Structure of Silicate Minerals

• Silica tetrahedron is the basic building block of all silicate minerals, composed of one silicon atom and four oxygen atoms in a tetrahedral arrangement.
• Silica tetrahedrons combine in different arrangements, such as chains and sheets, to form different silicate minerals.

Types of Silicates

• Nesosilicates (orthosilicates) are the simplest silicates, with silica tetrahedrons forming the base of the silicate minerals.
• Examples of nesosilicates include forsterite and tephroite.
• Sorosilicates are formed when two tetrahedrons are linked together by one oxygen atom.
• Cyclosilicates form chains that bend to form rings, with high hardness, luster, and durability.
• Inosilicates are long single and double chain silicates, with single and double chain structures.
• Phyllosilicates are formed when rings of tetrahedrons are linked by oxygens to other rings of tetrahedrons in a flat sheet-like structure.
• Tectosilicates (framework silicates) have a complex structure with tetrahedrons interconnected and extending outward in all directions.

Examples of Silicates

• Quartz is the second most abundant mineral in Earth's crust, made of oxygen and silicon, and formed when magma cools slowly.
• Feldspar is the most common mineral in Earth's crust, containing alumina and silica.
• Mica minerals are known as sheet silicates, with a two-dimensional sheet structure and perfect basal cleavage.
• Amphiboles are minerals that occur in many different rock types, with high silica content, and are usually dark in color and composed of silicates combined with metals.
• Olivine is a mineral found in dark igneous rocks, with high crystalline temperature, and is one of the first minerals to crystallize from Earth's heat.