Question

Select the correct statement : (1) Double chain silicates are known as amphiboles. (2) In cyclic silicates two oxygen atoms per tetrahedron are shared. (3) Orthosilicates contain discrete \(\left(\mathrm{SiO}_{4}\right)^{4-}\) units. (4) All of these

Short answer

The correct statement is (4) All of these.

Step-by-step solution

Understand the Question

The exercise asks to identify the correct statement(s) from a list of four options regarding types of silicates.

Option (1) Evaluation

Double chain silicates are also known as amphiboles. This statement is correct.

Option (2) Evaluation

In cyclic silicates, each tetrahedron shares two oxygen atoms with adjacent tetrahedrons. This statement is correct.

Option (3) Evaluation

Orthosilicates contain discrete \(\text{SiO}_4^{4-}\) units with no shared oxygen atoms. This statement is correct.

Option (4) Evaluation

Since all the previous statements have been evaluated as correct, option (4), stating 'All of these', is correct.

Key concepts

Double Chain Silicates

Double chain silicates, also known as amphiboles, play a significant role in mineralogy. They have complex structures where two single chains of tetrahedrons run parallel and are linked by sharing oxygen atoms. Amphiboles are typically found in metamorphic rocks and are known for their elongated crystal forms. The most common amphibole minerals include hornblende and tremolite. These minerals are often characterized by their hardness and resistance to weathering, making them crucial components in the Earth's crust.

Cyclic Silicates

Cyclic silicates, or ring silicates, have a unique structural pattern where each silicon-oxygen tetrahedron shares two oxygen atoms with its neighboring tetrahedrons. This arrangement forms ring-like structures, often with specific ratios of silicon to oxygen, such as 1:3. Examples of cyclic silicates include minerals like beryl and tourmaline, which are valued both for their beauty and industrial applications. Beryl, for instance, can appear as emerald when it contains trace amounts of chromium or vanadium, contributing to its vibrant green color.

Orthosilicates

Orthosilicates consist of discrete \((\mathrm{SiO_4})^{4-}\) units, meaning each tetrahedron is fully independent and not bonded to other silicon atoms. This results in minimal sharing of oxygen atoms. Minerals such as olivine, garnet, and zircon are classic examples of orthosilicates. These minerals are significant for their robust structure and resistance to high temperatures, contributing to their presence in both igneous and metamorphic rocks. The distinct bonding structure in orthosilicates leads to varied physical and chemical properties, offering broad applications in geology and other fields.

Amphiboles

Amphiboles belong to a broader classification of double chain silicates. They consist of two linked chains of silicon-oxygen tetrahedrons that form a complex three-dimensional network. This structural complexity gives amphiboles a range of physical properties, such as prismatic or needle-like crystal forms. Amphiboles are commonly found in metamorphosed rocks such as schists and gneisses. A distinguishing feature of amphiboles is their ability to contain various metal ions like iron, magnesium, and calcium within their structure, which can significantly affect their color and density.