Question

The silicates which contain discrete tetrahedral units are: (a) Ortho silicates (b) Sheet silicates (c) Three dimensional silicates (d) Pyrosilicate

Short answer

Ortho silicates (option a) contain discrete tetrahedral units.

Step-by-step solution

Understand Silicate Structures

Silicates are minerals composed of silicon and oxygen. The way silicon and oxygen atoms are arranged determines the type of silicate. There are various types based on their structure: ortho (or nesosilicates), sheet silicates, three-dimensional (or tectosilicates), and others like chain silicates.

Examine Ortho Silicates

Ortho silicates, also known as nesosilicates, have discrete tetrahedral units where each silicon-oxygen tetrahedron is isolated from the others. They are represented by the formula \[(SiO_4)^{4-}\] indicating isolated tetrahedra.

Analyze Other Options

Sheet silicates have a structure where tetrahedra are connected in sheets, while three-dimensional silicates have a fully interconnected framework. Pyrosilicates have pairs of tetrahedra sharing one oxygen atom.

Identify Discrete Tetrahedral Silicates

Based on the structure descriptions, ortho silicates are the ones with discrete tetrahedral units, as each silicate tetrahedron is independent.

Key concepts

Ortho Silicates

Ortho silicates, often referred to as nesosilicates, are a distinct group of silicate minerals characterized by their isolated tetrahedral structure. In an ortho silicate, the silicon-oxygen tetrahedra do not share any oxygen atoms with neighboring tetrahedra. This results in discrete units. Often, they are represented by the chemical formula \[(SiO_4)^{4-}\]. This formula indicates that each silicon atom is bonded to four oxygen atoms, forming a solitary tetrahedral unit.

In nature, these isolated tetrahedra contribute to unique properties seen in minerals such as olivine, garnet, and zircon. Because of their isolated nature, ortho silicates have distinct and specific physical and chemical properties compared to other types of silicates.

Key characteristics of ortho silicates include:

• Their isolated tetrahedral arrangement.
• Stability resulting from their solitary tetrahedral units.
• Distinct crystal structures, which influence their appearance and function.

Silicate Structure

Silicate minerals are primarily composed of silicon and oxygen, forming the foundation of most rocks and minerals on Earth. A silicate structure is determined by the arrangement of its silicon-oxygen tetrahedra. This structural element dictates how the silicate mineral behaves, looks, and reacts with other minerals.

Silicates can be divided into several categories based on how their tetrahedra are linked:

• Single Tetrahedra: Found in ortho or nesosilicates where each tetrahedron is isolated.


• Chain Silicates: Where tetrahedra link together in chains, such as in pyroxenes and amphiboles.


• Sheet Silicates: Characterized by layers of tetrahedra, typical of micas and clays.


• Framework Silicates: Tetrahedra form a three-dimensional network, as seen in quartz and feldspars.

Through these connections, silicate structures immensely influence a mineral's physical properties, such as hardness, cleavage, and stability. Each connection type offers varying characteristics, making each silicate structure unique.

Tetrahedral Units

The fundamental building blocks of silicate minerals are the silicon-oxygen tetrahedra. This unit comprises a silicon atom centrally coordinated by four oxygen atoms, forming a tetrahedral shape. The way these units link together decides the type and characteristics of the silicate mineral formed.

In silicate chemistry, tetrahedral units can exist in different configurations:

• Isolated Tetrahedra: As seen in ortho silicates, leading to discernible crystal structures.


• Simple Chains: Tetrahedra connect in long single or double chains, creating elongated mineral formations.


• Sheet Structures: Tetrahedra link in extensive two-dimensional layers, pertinent to mineral groups like micas.


• Frameworks: Tetrahedra interlock in a 3D lattice, providing a robust structure as evidenced in quartz.

These varied configurations contribute to the diversity of silicate minerals. The strength, density, and other attributes of minerals rely on their tetrahedral arrangements.