Some felsic rocks are and some are not. The term felsic is a description of an ingeous rock's composition, not its texture or where it occurs.
Felsic, high in silica. Mafic, low in silica. Intrusive, those formed underground. Extrusive, those formed above ground.
The igneous rocks that can be both intrusive and extrusive are known as porphyritic rocks. These rocks form when magma partially cools underground (intrusive) before being erupted onto the Earth's surface where the remaining magma cools quickly (extrusive). This dual cooling process creates distinctive textures in the rock, with larger crystals (phenocrysts) embedded in a finer-grained matrix.
A porphyritic igneous rock is one with a texture containing large isolated crystals (phenocrysts) in a mass of fine grained crystals . Porphyritic texture indicates that a magma has gone through a two stage cooling process. The magma has cooled sufficiently underground to allow some minerals to crystallize and grow in size; the magma is then expelled above ground where the remaining liquid magma solidifies quickly, allowing only small crystals to develop.
Recognized by a porphyritic texture, where large crystals (phenocrysts) are embedded in a fine-grained matrix. This indicates that the rock underwent two stages of cooling, with the phenocrysts forming during the slow cooling in the intrusive stage, followed by rapid cooling during the extrusive stage to form the fine-grained matrix.
No. Andesite is classed as an 'intermediate' rock, being halfway in composition between a mafic and felsic rock. Mafic rocks are those that contain alot of ferromagnesian minerals (iron and magnesium) which give mafic rocks their dark colouring. Typical ferromagnesian minerals include olivine and pyroxene. Typical mafic rocks are basalt and gabbro. Felsic rocks, on the other hand, are low in magnesium and iron and are usually light in colour, such as granite and rhyolite. Andesite therefore typically contains a mixture of both felsic and mafic minerals and is classed as 'intermediate'.
Felsic rocks can be either intrusive or extrusive. Intrusive felsic rocks form underground when magma cools and solidifies slowly, creating large crystals. Extrusive felsic rocks form at the Earth's surface when volcanic lava cools quickly, resulting in fine-grained rocks like rhyolite.
Igneous rocks exhibit three types of textures: coarse grained (intrusive), fine grained (extrusive), and porphyritic (two-stage solidification of mineral constituents). Chemically, they are categorized as felsic, mafic, or intermediate.
Rhyolite is a felsic extrusive igneous rock.
Felsic, high in silica. Mafic, low in silica. Intrusive, those formed underground. Extrusive, those formed above ground.
The three main groups of igneous rocks are intrusive (plutonic), extrusive (volcanic), and hypabyssal rocks. Intrusive rocks form below the Earth's surface from the slow cooling of magma. Extrusive rocks form on the Earth's surface from rapidly cooling lava. Hypabyssal rocks are intermediate rocks that form from magma that solidifies in the crust.
A felsic extrusive igneous rock, such as rhyolite or obsidian.
The igneous rocks that can be both intrusive and extrusive are known as porphyritic rocks. These rocks form when magma partially cools underground (intrusive) before being erupted onto the Earth's surface where the remaining magma cools quickly (extrusive). This dual cooling process creates distinctive textures in the rock, with larger crystals (phenocrysts) embedded in a finer-grained matrix.
Igneous rocks are generally classified first on the basis of their formation (and therefore their texture) as intrusive or extrusive. Intrusive rocks are solidified from magma under the surface resulting in a visible crystalline texture, and extrusive igneous rocks are solidified from lava at or near the surface, resulting in a small or nearly invisible crystalline texture.Igneous rock can additionally be classified by general chemistry composition as felsic, intermediate, mafic, and ultramafic. Felsic rocks are higher in silica and aluminum. Maficrocks are higher in magnesium and iron.Examples of igneous rock include:pumicebasaltandesitewehrlitemonzoniteanorthositewelded tuffnepheline syeniteaplitewebsteritekimberlitegabbrodioritegranitebasanitetroctolitepegmatitediabasepicritelatitegranodioritetonaliteperidotiteignimbritehornblenditelampophyrephonolitedunitesyenitetachylytemonzogranitetephritegranophyreboniniterhyodacitetrachytecarbonatiteharzburgiteicelanditepyroxenitetrachyandesitefoidoliterhyoliteobsidianscoriaWords used to describe igneous rock or igneous rock typesinclude: ultramafic, mafic, intermediate, felsic, aphanitic, porphyritic, phaneritic, extrusive, intrusive, vesicular, glassy, coarse grained, fine grained, acidic, basic.
A porphyritic igneous rock is one with a texture containing large isolated crystals (phenocrysts) in a mass of fine grained crystals . Porphyritic texture indicates that a magma has gone through a two stage cooling process. The magma has cooled sufficiently underground to allow some minerals to crystallize and grow in size; the magma is then expelled above ground where the remaining liquid magma solidifies quickly, allowing only small crystals to develop.
They are all extrusive igneous (i.e. volcanic) rocks of intermediate to felsic composition.
Rhyolite Porphyry is an intrusive rock, formed from the slow cooling of magma underground. It is characterized by large crystals (phenocrysts) surrounded by a fine-grained matrix.
Recognized by a porphyritic texture, where large crystals (phenocrysts) are embedded in a fine-grained matrix. This indicates that the rock underwent two stages of cooling, with the phenocrysts forming during the slow cooling in the intrusive stage, followed by rapid cooling during the extrusive stage to form the fine-grained matrix.