Nepheline syeniteNepheline syenite is a coarse-grained, plutonicigneous rock composed principally of alkali feldspar and the feldspathoid mineral nepheline. It is silica-undersaturated and therefore lacks primary quartz; phonolite is its fine-grained volcanic equivalent. Specimens are commonly pale grey or pink, although dark-green varieties also occur. PetrologyNepheline syenites are silica-undersaturated, and some are peralkaline.
FeldsparFeldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust and 41% of the Earth's continental crust by weight.
TrachyteTrachyte () is an extrusiveigneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrusions) enriched with silica and alkali metals. It is the volcanic equivalent of syenite.
MaficMafic is a term used in geology to describe silicate minerals, magmas, and igneous rocks that are rich in magnesium and iron, while being relatively low in silica content. Common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclasefeldspar. Mafic materials can also be described as ferromagnesian.
Intrusive rockIntrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form intrusions, such as batholiths, dikes, sills, laccoliths, and volcanic necks. Intrusion is one of the two ways igneous rock can form. The other is extrusion, such as a volcanic eruption or similar event. An intrusion is any body of intrusive igneous rock, formed from magma that cools and solidifies within the crust of the planet.
TAS classificationTAS stands for Total Alkali Silica. The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali and silica contents. These chemical parameters are useful because the relative proportions of alkalis and silica are important in determining both normative mineralogy and actual mineralogy. The classification can be simple to use for rocks that have been chemically analyzed.
FelsicIn geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Molten felsic magma and lava is more viscous than molten mafic magma and lava.
Extrusive rockExtrusive rock refers to the mode of igneousvolcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contrast, intrusive rock refers to rocks formed by magma which cools below the surface.
PorphyriticPorphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all types of igneous rocks can display some degree of porphyritic texture. Most porphyritic rocks have bimodal size ranges, meaning the rock is composed of two distinct sizes of crystal.
Intermediate compositionIn igneous petrology, an intermediate composition refers to a rock whose chemical composition is intermediate between felsic and mafic compositions, typically containing about 52–63 wt%SiO2. It is not an IUGS recognized term. Common intermediate volcanic rocks include andesite and trachyandesite, while common intermediate plutonic rocks include diorite and granodiorite.
Ancient GreekAncient Greek (Ἑλληνική, Hellēnikḗ [hellɛːnikɛ̌ː]) includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (c. 1400 – c. 1200 BC), Dark Ages (c. 1200 – c. 800 BC), the Archaic or Homeric period (c. 800 – c. 500 BC), and the Classical period (c. 500 – c. 300 BC).
AphaniteAphanites (adj. aphanitic; from Ancient Greekαφανης (aphanḗs)'invisible') are igneous rocks that are so fine-grained that their component mineralcrystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye), however visible using magnification (in contrast to Cryptocrystallines, in which the crystals are not visible even under microscope).*As an Amazon Associate I earn from qualifying purchases.