( ( Mafic rocks ) ( ( ( contain ( more silica ) ) ( than ( felsic rocks ) ) ) . ) )
(ROOT (S (NP (JJ Mafic) (NNS rocks)) (VP (VBP contain) (NP (JJR more) (NN silica)) (PP (IN than) (NP (JJ felsic) (NNS rocks)))) (. .)))
Mafic rocks contain more silica than felsic rocks.
(ROOT (S (NP (JJ Felsic) (NNS igneous) (NNS rocks)) (VP (VP (VBP contain) (NP (JJ felsic) (NNS minerals))) (, ,) (VP (ADVP (RB typically)) (VBP contain) (NP (NN aluminum) (CC and) (NN sodium))) (CC and) (VP (VBP are) (ADJP (JJ high) (PP (IN in) (NP (NN silica)))))) (. .)))
Felsic igneous rocks contain felsic minerals, typically contain aluminum and sodium and are high in silica.