In geology|lang=en terms the difference between igneous and orthogneiss
is that igneous is (geology) resulting from, or produced by, the action of great heat; with rocks, it could also mean formed from lava/magma; as, granite and basalt are igneous rocks while orthogneiss is (geology) a gneiss derived from an igneous rock.
As an adjective igneous
is pertaining to, having the nature of fire; containing fire; resembling fire; as, an igneous appearance.
As a noun orthogneiss is
(geology) a gneiss derived from an igneous rock.
igneous
English
Adjective
(
en adjective)
Pertaining to, having the nature of fire; containing fire; resembling fire; as, an igneous appearance
(geology) Resulting from, or produced by, the action of great heat; with rocks, it could also mean formed from lava/magma; as, granite and basalt are igneous rocks
orthogneiss
English
Noun
(es)
(geology) A gneiss derived from an igneous rock.