Question

Which is the amorphous form of silica?
A. Quartz
B. Tridymite
C. Onyx
D. Crystobalite

Answer 1

Amorphous solids are those solid which do not have a definite form. In amorphous solid, the solid does not arrange the atoms and molecules in a lattice. They are just opposite to crystalline forms of solid. Some crystalline forms of silica are quartz, tridymite, cristobalite and so on.

Complete answer:
Silica is the common name of silicon dioxide. It is made up of one silicon and two oxygen atoms. It has a chemical formula as $Si{O_2}$. It is also defined as a mineral composed of silicon and oxygen. Silica exists in various crystalline forms but it rarely exists in amorphous form. Silica exists in crystalline forms are quartz, tridymite, cristobalite and so on.
The amorphous form of silica is onyx and kieselguhr. Crystalline silica is highly toxic in nature if it is inhaled by converting it into powder form then it can lead to severe inflammation of the lung tissues. It can cause silicosis, bronchitis, lung cancer and systemic autoimmune disease. Systemic autoimmune diseases are lupus, rheumatoid arthritis. Similarly, the Inhalation of amorphous silicon dioxide, in high doses, leads to non-permanent short-term inflammation, where all effects heal.
So, Onyx is one of the amorphous forms of silica that is silicon dioxide.

Hence, option (C) is correct.

Note:
Silica is the primary ingredient in the production of most glass. As other minerals are melted with silica, the principle of Freezing Point Depression lowers the melting point of the mixture and increases fluidity. The glass transition temperature of pure silicon oxide is about $1475K$ . When molten silicon dioxide is rapidly cooled, it does not crystallize, but solidifies as a glass. Because of this, most ceramic glazes have silica as the main ingredient.