 Re: how to combine the two sentences?
Your original combined sentence:
Lava is made of silica, the same material of which sand and glass are composed of.
"Composed of" is a phrasal verb. "Composed" and "of" can be separated, so that "of" occurs next to the preposition "which": "of which". Or "composed of" can occur together. Only one "of" is needed. If the word "of" is used twice in this verb phrase, it is like saying "composed of of" even though the words are not next to each other in the sentence.
The sentence: "Sand and glass are composed of the same material of silica," has two instances of the word "of" because one "of" is part of the phrasal verb "composed of" and the second "of" is a preposition.
(That sentence is actually incorrect. The correct word there would have been "as": "Sand and glass are composed of the same material as silica.") |