Questions & Answers

Which of the following is an example of chain silicates?
(A) Kaolinite
(B) Zircon
(C) Bentonite
(D) Diopside

Answer Verified Verified
Hint: It is a rock-forming pyroxene mineral, with a chemical formula of ${ Ca }Mg\left[ { \left( Si{ O }_{ 3 } \right) }_{ 2 } \right] $ . It usually occurs in igneous and metamorphic rocks. Also, used for making gemstones.

Complete answer:
Chain silicates are often known as inosilicates.
Diopside is an example of chain silicates.
It has the chemical formula of ${ Ca }Mg\left[ { \left( Si{ O }_{ 3 } \right) }_{ 2 } \right] $.
Chain silicates consist of single chains of ${ \left( { SiO }_{ 3 }^{ 2- } \right) }_{ n }$ in which Si:O = 1:3 and double chains of ${ \left( { { Si }_{ 4 }O }_{ 11 }^{ 6- } \right) }_{ n }$ in which Si:O = 4:11.
Option (D) Diopside is the correct answer. Now, we can look at other options given in the question.
Option (A) Kaolinite, is a clay mineral of chemical formula ${ Al }_{ 2 }{ O }_{ 3 }\quad 2Si{ O }_{ 2 }.2{ H }_{ 2 }O$ has a structure of 1:1 uncharged dioctahedral layer structure where each layer consists of a single silica tetrahedral sheet and single octahedral sheet of alumina.
Option (B) Zircon, is a silicate mineral $\left( { ZrSiO }_{ 4 } \right) $, the principal source of Zr. Zircon is mostly known as an accessory mineral in acid igneous rocks. These silicates belong to the orthosilicate group.
Option (C) Bentonite, is a rare blue barium titanium cyclosilicate .These come under the category of cyclosilicates/polysilicates. Here each tetrahedron shares two of its oxygen atoms with other tetrahedrons and the rings formed are having three.
So, the correct answer is “Option D”.

Additional Information: Silica and silicates are the most abundant compounds on the earth’s crust(around 95%). Silicon dioxide $\left( { SiO }_{ 2 } \right) $ which is also known as silica is found in many crystallographic forms.
A big number of silicate units exists which are zeolites etc. The structure of silicate is${ SiO }_{ 4 }^{ 4- }$ , in which the four oxygen atoms are attached to one silicon atom. When a silicate unit is joined together it forms a ring, chain as well as 3-D structure. Glass and cement are examples of man-made (artificial) silicates.
${ SiO }_{ 4 }^{ 4- }$ tetrahedron is the basic building block of all silicate minerals.
The formula of silicate sheet is ${ \left( { { Si }_{ 2 }O }_{ 5 }^{ 2- } \right) }_{ n }$, Silicate minerals containing sheets are termed phyllosilicates.

Note: Among chain silicates, there are single and double chain silicates. Asbestos, augite (minerals in the pyroxene family) are examples of single chain silicates. Amphibole and Hornblende are examples of double chain silicates.