Corundum: Properties and Uses

Corundum is a naturally occurring crystalline form of aluminum oxide, with the chemical formula Al₂O₃. It is one of the hardest minerals on Earth, ranking 9 on the Mohs scale of mineral hardness, just below diamond. Corundum can occur in a variety of colors, with red corundum known as ruby, and all other colors (including blue, yellow, and pink) collectively referred to as sapphire.

Properties of Corundum:

Hardness: 9 on the Mohs scale, making it extremely durable and suitable for use in various industrial applications.
Color: Occurs in a wide range of colors, with the most valuable being red (ruby) and blue (sapphire).
Transparency: Can be transparent to opaque, depending on the impurities present in the crystal lattice.
Luster: Typically exhibits a vitreous to adamantine luster.
Crystal System: Hexagonal crystal structure, often forming prismatic or tabular crystals.

Uses of Corundum:

Due to its hardness and resistance to chemical attack, corundum has several practical applications:

As an abrasive, in the form of emery or as a component of sandpaper and grinding materials.
In the manufacture of refractory materials, such as firebrick, due to its high melting point and resistance to heat.
In the production of synthetic gemstones, including rubies and sapphires used in jewelry.
As a component in specialized optical instruments due to its high hardness and optical properties.

Study Guide for Corundum:

When studying corundum, it is important to focus on the following aspects:

Crystal Structure: Understand the hexagonal crystal system and the typical forms of corundum crystals.
Hardness and Mohs Scale: Learn about the exceptional hardness of corundum and its ranking on the Mohs scale in comparison to other minerals.
Color Variations: Explore the causes of different color variations in corundum, particularly the distinction between ruby and sapphire.
Applications: Investigate the industrial and commercial uses of corundum, including its role in abrasives, refractory materials, and gemstone production.

By understanding the properties and uses of corundum, you will gain a comprehensive insight into this important mineral and its significance in various fields of science and industry.