( ( as ( building materials ) ) . )
(ROOT (FRAG (PP (IN as) (NP (NN building) (NNS materials))) (. .)))
as building materials.
(ROOT (S (NP (DT A) (NN mineral)) (VP (VBZ is) (VP (VBN described) (PP (IN as) (NP (NP (DT a) (JJ solid) (JJ natural) (NN material)) (PP (IN with) (NP (DT a) (NN crystal) (NN structure))))))) (. .)))