I am thinking. It is not an easy question.
To say that human is made of carbon is not correct either. The best way to say it is that human is made of oxides. However, if you will, silicates is also a type of oxides. (definition of oxide: anything contains oxygen)
So, unless we spell out the exact chemical composition of a human being, we will give a wrong answer anyway. And I know for sure that every human, or even every life, would have different composition (to the third decimal of all elements).
God intends to use "material" to make human beings (unlike angels). So, the consideration is that what kind of material is the best choice? Whether the created being would operate based on the property of that material may not be the most important consideration. Because magic is gong to happen anyway in making that object become alive.
Using silicates to make Adam, could only mean to use "the most common earth material" to make Adam, instead of using Jupiter's material (which could probably be more realistic). So Adam belongs to the earth which is also God's unique creation.