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:

1. Crystal Structure: Understand the hexagonal crystal system and the typical forms of corundum crystals.
2. Hardness and Mohs Scale: Learn about the exceptional hardness of corundum and its ranking on the Mohs scale in comparison to other minerals.
3. Color Variations: Explore the causes of different color variations in corundum, particularly the distinction between ruby and sapphire.
4. 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.