Cristobalite

B-cristobal1

B-cristobal2

A-cristobal

Α-Cristobalite

Β-Cristobalite

Cristobalite is a mineral polymorph of silica that is formed at very high temperatures. It is found in volcanic rocks and is known for its high-temperature stability, making it of interest in a variety of industrial applications. Unlike its more common counterpart, quartz, cristobalite undergoes a significant volume expansion upon heating, which can lead to cracking in materials that incorporate it, such as ceramics and refractory materials.

Properties

Cristobalite exists in two crystal forms: the low-temperature form, which is stable up to 1470°C, and the high-temperature form, which is stable above this temperature. The transition between these forms is reversible but involves a significant change in volume. This characteristic is critical in applications where thermal stability and shock resistance are important. Cristobalite has a Mohs hardness of 6-7, making it less hard than quartz. Its specific gravity is approximately 2.32, which is slightly lower than that of quartz.

Formation

Cristobalite forms from silica-rich volcanic rocks through the devitrification of volcanic glass. This process can occur naturally in lava flows that cool rapidly on the earth's surface or in the laboratory under controlled conditions. The formation of cristobalite is influenced by factors such as temperature, pressure, and the presence of other minerals, which can act as catalysts.

Applications

Due to its thermal properties, cristobalite is used in the manufacture of kiln furniture, such as setters and saggers, which are used to hold and support ceramics during firing. It is also used in the production of investment casting shells, where its volume stability at high temperatures ensures the accuracy of the cast parts. In addition, cristobalite is used as a filler in paints, coatings, and plastics, where it enhances properties such as scratch resistance and surface finish.

Health Risks

Inhalation of cristobalite dust can pose health risks, as it is a form of respirable crystalline silica. Prolonged exposure to respirable silica dust can lead to silicosis, a serious lung disease, as well as other respiratory illnesses. Therefore, occupational safety measures are important in industries that process or use cristobalite.

See Also

• Silica
• Quartz
• Mineral polymorphism
• Volcanic rock
• Refractory materials