how to combine the two sentences?

[mengta]

Lava is made of silica.
Sand and glass are composed of the same material of silica.

is the following sentence correct?

Lava is made of silica, the same material of which sand and glass are composed of.

thanks

[grammar.gal]

You are very close! The only problem is that you used the word "of" twice. You can fix it by taking out one "of":

1 (Formal) - "Lava is made of silica, the same material of which sand and glass are composed."

2 (Informal) - "Lava is made of silica, the same material which sand and glass are composed of."

Both formal and informal sentences are fine, but the formal sentence is more widely accepted as correct. It would also be correct to take out the word "same":
3- "Lava is made of silica, the material of which sand and glass are composed."

[mengta]

to omit the "of" was what confused me.

Lava is made of silica.
Sand and glass are composed of the same material of silica.

there are two "of" in the second sentence.
why do we have only one "of" in the combined sentence?
thanks

[grammar.gal]

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.")

[Temico]

Lava is made of silica.
Sand and glass are composed of the same material of silica.

"Lava is made of silica, the same material which is comprised in sand and glass."
or
"Lava is made of silica which is the same material comprised in sand and glass."

(Both above sentences avoid repeating "of" in the subordinate clause.)

[grammar.gal]

Originally Posted by Temico

"Lava is made of silica, the same material which is comprised in sand and glass."
or
"Lava is made of silica which is the same material comprised in sand and glass."

(Both above sentences avoid repeating "of" in the subordinate clause.)

I'm sorry, but that is not correct. The word "comprised" does not mean the same thing as "composed of".


Use this sentence. It is correct. This is what a native speaker would say, and it is correct according to modern grammars.
"Lava is made of silica, the same material which sand and glass are composed of."

[Temico]

The word "comprised" does not mean the same thing as "composed of".

If "comprised of" does not mean "be composed of/ made up of", what does it mean then, may I ask?

[grammar.gal]

I apologize. The reason "comprised" does not work in that sentence is a usage problem. The definition of "comprise" is often given as: "composed of". However, the two are not interchangeable. One does not use "comprise" in exactly the same way that one used "composed of."

The way Temico used the word "comprised" is incorrect, but I gave the wrong reason for the incorrectness. Instead of saying they have different meanings, I should have said they have different uses.


A usage note on "compose" in The New Oxford American Dictionary:
"Compose and comprise are often confused, but can be sorted out. The parts compose (make up) the whole; the whole comprises (contains) the parts: citizens who have been been chosen at random and screened for prejudices compose a jury; each crew comprises a commander, a gunner, and a driver. In passive constructions, the whole is composed of the parts, and the parts are comprised in the whole. In other words, ( compose = put together; comprise = contain, consist of.) Usage of the phrase 'is comprised of' is avoided by careful speakers and writers."

But this thread is not a debate of "comprise" vs "composed of".

[Temico]

( compose = put together; comprise = contain, consist of.) Usage of the phrase 'is comprised of' is avoided by careful speakers and writers."

First of all, thanks for the quick reply.
Second, let's substitute(as per above explantion) "contained in" for "comprised in" in my sentences:-

a) Lava is made of silica, the same material which is contained in in glass and sand.

b)Lava is made of silica which is the same material contained in sand and glass."

Do you still insist that my usage is incorrect??

Just to let you know that I am quite aware of the difference between "comprised of" and "comprised in" and also, I didn't write "Lava is made up of silica which is the same material sand and glass are comprised of"