Syenites are products of alkaline igneous activity, generally formed in thick continental crustal areas, or in Cordilleran subduction zones. The formation of syenites can be theorized to be from the melt of granitic or igneous protolith to a fairly low degree of partial melting.

变正长岩 (episyenite)为一种由热液蚀变作用形成的成分与正长岩近似的岩石，原岩为花岗质岩石。 在蚀变过程中，碱性溶液先溶离了石英，然后在空洞中析出碱性长石、蠕绿泥石、新生石英和方解石等，形成富碱性长石的，大体保持原花岗岩结构的变正长岩。 [1] 主要矿物为 碱性长石 和斜长石，次要矿物为暗色矿物、石英、似长石。 副矿物有磷灰石、磁铁矿、榍石、锆石等。 碱性长石：有正长石、微斜长石、条纹长石、歪长石、An<5%的钠长石。 晶体呈板状外形或它形，为 …

2023年10月20日 · Syenite is a coarse-grained, plutonic (intrusive) igneous rock that primarily consists of the minerals feldspar, typically orthoclase feldspar, and often includes smaller amounts of other minerals such as hornblende, mica, or amphibole. Unlike granite, which is another common intrusive igneous rock, syenite contains minimal to no quartz. The ...

Syenite, any of a class of intrusive igneous rocks essentially composed of an alkali feldspar and a ferromagnesian mineral. A special group of alkali syenites is characterized by the presence of a feldspathoid mineral such as nepheline, leucite, cancrinite, or sodalite (see nepheline syenite).

2023年7月6日 · Syenite is a coarse-grained, mostly light-colored intrusive rock with an intermediate to felsic composition. It has mainly alkali feldspar, lesser plagioclase, and one or more mafic minerals. Also, it may have a small amount of quartz.

Syenite is a type of plutonic rock or we can mention a type of intrusive igneous rocks. Intrusive Igneous are those rocks that are formed beneath the surface in the crust. This rock mainly consists of ferromagnesian minerals and alkali feldspar & has a coarse-grained texture because magma cools slowly inside.

Syenites are holocrystalline coarse- to medium-grained intermediate igneous rocks in which the dominant mineral is alkali feldspar.

Syenite is an igneous rock that solidified slowly in the crust in a similar manner to granite. A true syenite (sensu stricto) is also compositionally resembling granite. The most notable difference is the absence or very low quantity of quartz while it is an essential component of granite.

碱性正长岩（alkali feldspar syenite）又称含副长石碱性正长岩（foid bearing alkali syenite），是一种以碱性长石为主，而暗色矿物为碱性辉石或碱性角闪石的正长岩。

Syenite is an intrusive igneous rock composed primarily of alkali feldspar, lesser amounts of of plagioclase feldspar, and under 20% quartz. It is coarse-grained with tightly interlocking crystals. Syenite is usually off-white, gray, greenish, red, or pink with black spots and no …