The feldspar component of syenite is predominantly alkaline in character. Plagioclase feldspars may be present in small quantities, less than 10%.
Syenites are usually peralkaline and peraluminous, with high proportions of alkali elements and aluminium.
Syenites are formed from alkaline igneous activity, generally formed in thick continental crustal areas, or in Cordilleran subduction zones. To produce a syenite, it is necessary to melt a granitic or igneous protolith to a fairly low degree of partial melting. This is required because potassium is an incompatible element and tends to enter a melt first, whereas higher degrees of partial melting will liberate more calcium and sodium.