Petrology textures

ESA Logo

fossils and expeditions...

Petrology textures - a microscopic guide to classic rock textures

Petrographic rock identification

pegmatite Granitic Pegmatite - crystals over1cm tonaliteTonalite - hornblende, plagioclase clinopyroxene, biotite, and quartz. Notice how the hornblende rims the small core of relict clinopyroxene in the center anorthositeAnorthosite - almost entirely of albitic plagioclase. nepheline syeniteNepheline Syenite - plagioclase, microcline and nepheline myrmekiteIgneous plutonic microtexture - Myrmekite - wormy (rounded) intergrowths of quartz and K-feldspar in plagioclase. amygdaloidal textureVolcanic microtextures - Amygdaloidial texture - hydrothermal alteration of vesicles in scoria - open vesicle which has been filled with a secondary mineral(s) sandstone textureSandstone texture quartzite textureQuartzite texture crenulation cleavagesCrenulation cleavages - micaceous mineral differentiation that are coincident with the limbs of microfolds sandstone texture Clastic sandstone texture
biotite graniteBiotite Granite - quartz, plagioclase, biotite, and K-feldspar. dolerite (diabase) Dolerite - grain size more or less transitional between gabbro (coarse) and basalt (fine) - elongate lath-shaped plagioclase, colorful clinopyroxene clinopyroxenite Clinopyroxene - mostly the clinopyroxene augite. syenite Syenite - plagioclase and clinopyroxene, with biotite and heavy residual of K-Feldspar. volcanic breccia Volcanic microtexture Volcanic Breccia - tiny angular fragments of volcanic material spherulitesVolcanic microtextures - Spherulites - radiating masses of fibrous crystals in a glassy matrix textures of regional metamorphism  reaction rim Reaction rim - olivine on left, plagioclase on right, conglomerate textureClastic conglomerate texture serpentinisation Serpentinisation - irregular linear alteration of olivine (O) to serpentine (S)
granophyreGranophyre - micrographic quartz and K-feldspar (cuneiform shaped intergrowths) gabbro Gabbro - plagioclase and hypersthene (orthopyroxene) bronzititeBronzitie - orthopyroxenite - almost all hypersthene poikilitic (ophtic)Igneous macrotexture - Poikilitic (ophitic) texture komatiite (spinifex)Volcanic microtexture - Komatiite - Spinifex Texture - "spinifex texture" defined by extremely acicular olivine phenocrysts vitrophyric texture - obsidian glass Vitrophyre - phenocryst bearing obsidian textures of regional metamorphism sub-grains in quartz Sub-grains in quartz - formed during recrystallisation snowball garnet"Snowball" garnet - showing crystal rotationcoarse schist limestone with shellLimestone with shell
rhyoliteRhyolite - phenocrysts of quartz, K-feldspar (sanidine), plagioclase, and biotite in a fine-grained groundmass noriteNorite - a gabbro in which the pyroxene is principally orthopyroxene. duniteDunite -almost all olivine perthite Igneous plutonic microtexture - Perthite - plagioclase exsolution lamellae in gray K-feldspar  -form as an originally homogeneous feldspar exsolves into two feldspars  scoria with vesicles Volcanic microtexture - Scoria with vesicles - highly-vesicular "frothy") basalt - black, ovals features are vesicles textures of contact metamorphism fine grained schist foliations due to shear force sericitic alterationSericitic alteration - feldspars have been largely replaced by fine-grained white sericite micasaussuritizationSassuritization - weak alteration of the plagioclase feldspar - the grain is also rimmed by fine grained iron-oxyhydroxide precipitating from solution.