Silicate Mineral Structures and the Geological Rock Cycle

Posted on Aug 19, 2026 in Geology

Silicate Materials and Mineral Structures

Week 7: Silicate materials contain silicon and oxygen and make up 90% of all minerals. The fundamental building block is the silicon tetrahedron (SiO4), often found in silica (SiO2).

Common Silicate Mineral Groups

  • Olivine: A silicate mineral group with isolated tetrahedra, common in ultramafic and mafic rocks.
  • Isolated tetrahedra: A silicate structure in which silica tetrahedra do not share oxygen with each other.
  • Pyroxene: A silicate mineral group with a single-chain structure.
  • Single-chain silicate: A silicate structure in which tetrahedra share oxygen to form chains.
  • Amphibole: A silicate mineral group with a double-chain structure; commonly contains OH.
  • Double-chain silicate: A silicate structure made of two linked chains of silica tetrahedra.
  • Sheet silicate: A silicate structure in which tetrahedra form sheets.
  • Mica: A sheet silicate mineral group with one strong direction of cleavage.
  • Chlorite: A green hydrous sheet silicate commonly associated with low-grade metamorphic rocks such as greenstone.
  • Framework silicate: A silicate structure in which tetrahedra are connected in a three-dimensional framework.
  • Quartz: A framework silicate made of silicon and oxygen, with the chemical formula SiO2.
  • Feldspar: A framework silicate mineral group that commonly contains aluminum and cations such as sodium, potassium, or calcium.

Structural Units and Bonding

  • I-beam: A structural unit in single-chain and double-chain silicate minerals, made of chains of silica tetrahedra facing each other with cations in between. I-beams are relatively strong internally, but bonds between neighboring I-beams are weaker, helping explain cleavage in pyroxene and amphibole.
  • T-O-T sheet: A sheet-silicate structure made of one octahedral layer between two tetrahedral layers. The tetrahedral sheets face inward toward the octahedral layer. T-O-T sheets are relatively strong internally, but bonds between neighboring T-O-T sheets are weaker, helping explain why minerals such as mica split into thin sheets.
  • Silicon-oxygen-silicon bridge: A connection between two silica tetrahedra through a shared oxygen.
  • Non-bridging oxygen: An oxygen in a silica tetrahedron that is not shared with another tetrahedron.
  • Polymerization: The degree to which silica tetrahedra are linked together.

Magma and Crystallization Processes

  • Silica content: The amount of SiO2 in a mineral, rock, or magma.
  • Fractional crystallization: The process in which minerals crystallize from magma at different temperatures, changing the composition of the remaining melt.
  • Partial melting: The process in which only part of a rock melts, often producing melt with a different composition from the original rock.
  • Mafic magma: Magma with relatively low silica content and higher magnesium and iron content; usually less viscous.
  • Felsic magma: Magma with higher silica content; usually more viscous.
  • Viscosity: Resistance to flow.

Metamorphic Rocks and Hydrous Minerals

  • Hydrous mineral: A mineral that contains water or OH– groups in its structure.
  • Greenstone: A low-grade metamorphic rock commonly formed from basalt and containing green hydrous minerals such as chlorite.
  • Amphibolite: A metamorphic rock rich in amphibole, commonly formed from basalt or gabbro at a higher metamorphic grade than greenstone.
  • Eclogite: A high-pressure metamorphic rock commonly containing garnet and pyroxene.
  • Garnet: A dense silicate mineral commonly associated with medium- to high-grade metamorphic rocks.
  • Dehydration: A metamorphic reaction in which hydrous minerals break down and release water.

Non-Silicate Mineral Categories

  • Non-silicate mineral: Minerals other than silicate minerals.
  • Carbonate mineral: A mineral containing the carbonate group, such as calcite or dolomite.
  • Calcite: A carbonate mineral with the chemical formula CaCO3.
  • Dolomite: A carbonate mineral containing calcium, magnesium, carbon, and oxygen.
  • Evaporite mineral: A mineral formed by precipitation from evaporating water.
  • Halite: An evaporite mineral with the chemical formula NaCl.
  • Metallic mineral: A mineral with metallic luster, commonly rich in metals.
  • Ore mineral: A mineral that contains a valuable element that may be economically extracted.
  • Magnetite: An iron-rich oxide mineral.
  • Hematite: An iron-rich oxide mineral commonly showing a reddish-brown streak.
  • Galena: A lead sulfide mineral.
  • Sphalerite: A zinc sulfide mineral.

Physical Properties and Identification

  • Color: The visible color of a mineral in a hand sample.
  • Streak: The color of a mineral in powdered form.
  • Streak plate: A plate used to produce a mineral powder for observing streak.
  • Luster: The way light reflects from a mineral surface.
  • Metallic luster: A shiny, metal-like reflection.
  • Vitreous luster: A glassy luster.
  • Crystal shape: The external shape of a mineral crystal, influenced by internal crystal structure.
  • Cleavage: The tendency of a mineral to break along planes of weakness.
  • Weak plane: A plane in a crystal structure where bonds are relatively easier to break.
  • Hardness: A mineral’s resistance to scratching.
  • Mohs hardness scale: A relative hardness scale from 1 to 10 based on which minerals can scratch other minerals.
  • Talc: The softest mineral on the Mohs scale.
  • Gypsum: A soft mineral that can be scratched by a fingernail.
  • Calcite: A carbonate mineral with a hardness of 3 on the Mohs scale.
  • Quartz: A hard mineral with a hardness of 7 on the Mohs scale.
  • Diamond: The hardest mineral on the Mohs scale.
  • Vickers test: A quantitative hardness test involving indentation by a diamond tip.

The Geological Rock Cycle

  • Rock cycle: The set of processes that connect igneous, sedimentary, and metamorphic rocks.
  • Igneous rock: Rock formed by the cooling and crystallization of magma or lava.
  • Sedimentary rock: Rock formed from sediments, chemical precipitates, or biological materials.
  • Metamorphic rock: Rock formed by the solid-state transformation of pre-existing rock under elevated pressure and temperature.
  • Parent rock: The original rock before metamorphism.
  • Sediment: Loose particles produced by weathering and erosion.