Structure refers to the size, shape, and arrangement of mineral grains. Granite is typically characterized by a crystalline granitic structure with semi-idiomorphic-idiomorphic mineral grains, coarse grain size, and time-crystallized (accessory minerals crystallize first, followed byz filling the gaps). The main types include:
- By grain size:
Fine-grained structure: Mineral grains with a diameter of <1mm, with delicate texture (such as the Niuchangshan rock mass). Medium-grained structure: Grains with a diameter of 1-5mm, with a uniform (common in most granite bodies). Coarse-grained structure: Grains >5mm, some reaching centimeter level, with a loose texture (such as Jingzhen granite).
Special structure types:
Porphyritic structure: Contains larger phenocrysts (e.g., potassium feldspar, diameter1cm) embedded in a fine-grained matrix (such as the specimen from Heihe City).
Porphyritic structure: A natural transition in grain size betweenocrysts and matrix.
Vuggy structure: Develops holes in the rock, filled with quartz or feldspar crystals.
Gneissic structure:covite and other sheet-like minerals are arranged in a directional manner (affected by tectonic deformation).
هيكل الجرانيت
Structure refers to the overall mineral distribution of the rock. Granite is dominated by massive structure:
Massive structure: Minerals (quartz, feldspar, muscovite) are evenly distributed and have directional arrangement, accounting for the majority of granite.
Other rare structures:
Spheroidal structure: Minerals aggregate in a spherical shape (such as some metamorph granite).
Porphyritic structure: Mineral distribution is uneven, with local enrichment.
Formation mechanism
Structural differences stem from the rate of magma and depth: slow cooling in a deep-seated environment (>3km underground) forms medium-coarse-grained structure; rapid cooling or magma mixing can lead toorphyritic/fine-grained structure (such as the injection of mafic magma producing perthite).
