1. feldspathoid - Noun
2. feldspathoid - Adjective
feldspathoid (countable and uncountable, plural feldspathoids)
(mineralogy) Any of a small group of igneous, plutonic, and volcanic minerals formed in magma that did not contain enough silica to satisfy all the chemical bonds. Feldspathoids are silica-poor variants of the feldspar group.
feldspathoid (not comparable)
(mineralogy) Resembling a feldspar.
Rare feldspathoid -rich mafic rocks, akin to alkali basalts, may have Na 2 O + K 2 O contents of 12% or more. Source: Internet
Except these last, practically all rocks contain felspars or feldspathoid minerals. Source: Internet