Question

Which of the following is not an amorphous form of silica? (1) Kieselghur (2) Agate (3) Jaspar (4) Crystoballite

Short answer

Crystoballite

Step-by-step solution

Understand Amorphous and Crystalline Forms

Amorphous materials lack a long-range order of a crystal lattice. Crystalline materials have a well-defined, repeating atomic structure.

Identify Amorphous Forms of Silica

Common amorphous forms of silica include Kieselghur, Agate, and Jasper. These materials do not have a well-defined crystalline structure.

Identify Crystalline Forms

Cristobalite is a known crystalline form of silica, meaning it has a distinct and regular atomic arrangement.

Answer the Question

Since Cristobalite has a crystalline structure and is not amorphous, it is the correct answer to the question.

Key concepts

Amorphous Materials

Amorphous materials are substances that do not have a long-range order in their atomic or molecular structure. This means that the atoms or molecules within an amorphous material are arranged more randomly, without the repeating pattern seen in crystalline structures.

Examples of amorphous materials include glass, plastics, and gels. Because of their disordered arrangement, these materials usually lack distinct shape and can exhibit different properties compared to their crystalline counterparts.

• No well-defined edges or faces
• Lack of a recognizable geometric pattern
• May appear glassy or transparent

Understanding amorphous materials helps in recognizing why some forms of silica, like Kieselghur, Agate, and Jasper, do not have the regular atomic structure found in crystals.

Crystalline Structures

Crystalline materials are characterized by their highly ordered atomic arrangement. In a crystalline structure, atoms are positioned in a specific, repeating pattern that extends in all directions. This repeating pattern is known as a crystal lattice.

Because of their ordered structure, crystalline materials tend to have sharp edges and well-defined faces. Common examples include salt, quartz, and metals.

• Well-defined geometric shapes
• Repetitive atomic arrangement
• Distinct melting points

Crystalline structures generally exhibit higher stability and can be identified by their unique structural patterns. Cristobalite is an example of a crystalline form of silica with a distinct and orderly atomic arrangement, which sets it apart from amorphous forms like Kieselghur, Agate, and Jasper.

Silica Forms

Silica is a compound made of silicon and oxygen, commonly found in nature. It exists in various forms, both amorphous and crystalline.

Amorphous forms of silica include:

• Kieselghur: A naturally occurring form of amorphous silica, often used in filtration and as a mild abrasive.
• Agate: A variety of chalcedony, Agate is a type of amorphous silica that is typically banded in appearance.
• Jasper: Another variety of chalcedony, Jasper is an opaque, highly colored form of amorphous silica.

Crystalline forms of silica include:

• Cristobalite: A crystalline form of silica that typically forms at high temperatures. It has a distinct, ordered atomic structure.
• Quartz: The most common crystalline form of silica, found extensively in the Earth's crust.

Recognizing the difference between these forms is crucial for various industrial applications and scientific studies, highlighting the versatility of silica in both amorphous and crystalline states.