Question

Which of the following is example of cyclic silicate?

• A. dioptase $\text{Cu}_6\text{Si}_6\text{O}_{18}.6\text{H}_2\text{O}$
• B. Crocidolite $\text{Na}_2\text{Fe}_5(\text{OH})_2[(\text{Si}_4\text{O}_{11})]_2$
• C. Serpentine $\text{Al}_2(\text{OH})_2\text{Si}_4\text{O}_{10}$
• D. Catapleite $\text{Na}_2\text{ZrSi}_3\text{O}_9.\text{H}_2\text{O}$

Answer 1

Answer: (A)

dioptase $\text{Cu}_6\text{Si}_6\text{O}_{18}.6\text{H}_2\text{O}$

Answer 2

Cyclic silicates, also known as ring silicates, are characterized by the cyclic arrangement of $\text{SiO}_4$ tetrahedra. These rings are formed by sharing two oxygen atoms between adjacent tetrahedra. The general formula for the silicate anion in cyclic silicates is $(\text{SiO}_3)_n^{2n-}$, where n is the number of tetrahedra in the ring, typically n=3, 4, or 6. This formula implies a Si:O ratio of 1:3 in the silicate anion.

• Dioptase $\text{Cu}_6\text{Si}_6\text{O}_{18}.6\text{H}_2\text{O}$: The silicate anion is $\text{Si}_6\text{O}_{18}$. The ratio of Si:O is 6:18 = 1:3. This fits the general formula $(\text{SiO}_3)_6^{12-}$, corresponding to a six-membered ring structure. Thus, Dioptase is a cyclic silicate.

• Crocidolite $\text{Na}_2\text{Fe}_5(\text{OH})_2[(\text{Si}_4\text{O}_{11})]_2$: The silicate anion is $(\text{Si}_4\text{O}_{11})_2 = \text{Si}_8\text{O}_{22}$. The ratio of Si:O is 8:22 = 4:11. This corresponds to double chain silicates (amphiboles), not cyclic silicates.

• Serpentine $\text{Al}_2(\text{OH})_2\text{Si}_4\text{O}_{10}$: The silicate anion is $\text{Si}_4\text{O}_{10}$. The ratio of Si:O is 4:10 = 2:5. This corresponds to sheet silicates (phyllosilicates), not cyclic silicates.

• Catapleite $\text{Na}_2\text{ZrSi}_3\text{O}_9.\text{H}_2\text{O}$: The silicate anion is $\text{Si}_3\text{O}_9$. The ratio of Si:O is 3:9 = 1:3. This fits the general formula $(\text{SiO}_3)_3^{6-}$, corresponding to a three-membered ring structure. Thus, Catapleite is also a cyclic silicate.

Based on the analysis, both Dioptase and Catapleite are examples of cyclic silicates. However, Dioptase, containing the $\text{Si}_6\text{O}_{18}$ ring, is a well-known example.