( There ( ( ( is ( no requirement ) ) ( that ( ( the ( mineral substances ) ) ( ( be naturally ) occurring ) ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (VBZ is) (NP (DT no) (NN requirement)) (SBAR (IN that) (S (NP (DT the) (NN mineral) (NNS substances)) (VP (VBP be) (ADVP (RB naturally)) (VP (VBG occurring)))))) (. .)))
There is no requirement that the mineral substances be naturally occurring.
(ROOT (S (NP (DT A) (NN mineral)) (VP (VBZ is) (VP (VBN described) (PP (IN as) (NP (NP (DT a) (JJ natural) (NN substance)) (SBAR (WHNP (WDT that)) (S (VP (VBZ makes) (PRT (RP up)) (NP (NNS rocks))))))))) (. .)))