Geological Textures PDF

# Texture ## Factors of crystal size: - Amount of dissolved gases - Cooling rate ## Temperature ↑ Cooling rate ↑ ## Texture: Shape, size, appearance of mineral grains ### Plutonic - Very coarse ### Pegmatitic texture - It's formed in the final stages of crystallization of magma rich with water...

# Texture ## Factors of crystal size: - Amount of dissolved gases - Cooling rate ## Temperature ↑ Cooling rate ↑ ## Texture: Shape, size, appearance of mineral grains ### Plutonic - Very coarse ### Pegmatitic texture - It's formed in the final stages of crystallization of magma rich with water vapor and gases. - Very coarse - Coarse grained texture - Cooling rate is slow - **Ex: Granite** # Volcanic ## Fine grained texture - Size is small - **Ex: Basalt rock** ## Amygdaloidal texture - Deposition of magma in voids/vesicles - **Amygdaloidal** ## Glassy texture - No crystals - Very rapid cooliing - **Ex: Obsidian** ## Vesicular texture - Evaporation of gases from magma during crystallization ## Trachytic texture - Tabular grained (phenocryst) - **Find ground mass** # Hypabyssal ## Medium grained texture - Porphyritic ## Chemical composition ### Acidic #### Felsic/Non ferromagnesium silicate - Si 65-80 - Rich (K-feldspar- Na-plag -mica- Qz ) - High viscosity - Low density - Light colour except 10% dark - **Ex: Granite** ### Basic - Ca - Acidic # Intermediate rock - Si 52-65 - Color - dark - Biotite - Pyroxene - Amphibole - **Ex: Andesite** # Basic - Mafic rock - Ferro magnesium silicate - Si 45-52 - Rich olivine, pyroxene, Ca-plag - Dark colour - High density - **Ex: Basalt** # Ultra Mafic rock - Si < 45 - Rich (olivine - pyroxene) - **Ex: Peridotite** ## Mineralogical ### Felsic - Non ferro Mg - Qtz - K-Feldspar - Na-plag - SiO2- K- Na ### Mafic - Ferro Mg - Olivine - Pyroxene - Amphibole - Biotite