Corundum

Definition

Corundum is a crystalline form of aluminum oxide (Al$_2$O$_3$) that naturally occurs in two gem-quality varieties: sapphire and ruby. It is known for its exceptional hardness, ranking 9 on the Mohs scale, making it the second hardest mineral after diamond. This characteristic allows corundum to be utilized in various applications, including abrasives and gemstones, and plays a significant role in phase identification and quantification using diffraction techniques.

5 Must Know Facts For Your Next Test

1. Corundum is often found in metamorphic rocks, such as schist and gneiss, and can also form through igneous processes.
2. The presence of trace elements like chromium in corundum produces the red color characteristic of rubies, while iron and titanium can create blue sapphires.
3. In addition to its natural forms, synthetic corundum can be produced in labs for use in jewelry and industrial applications.
4. Corundum's high hardness makes it useful not only as a gemstone but also as an abrasive material for grinding and cutting tools.
5. X-ray diffraction techniques are crucial for identifying corundum in geological samples by analyzing its unique diffraction pattern.

Review Questions

• How does the crystalline structure of corundum contribute to its physical properties, particularly hardness?
  • The crystalline structure of corundum features a hexagonal close-packed arrangement of oxygen atoms with aluminum atoms occupying interstitial sites. This dense packing contributes to its exceptional hardness, allowing it to resist scratching from most materials. The strong ionic bonds between aluminum and oxygen also play a vital role in giving corundum its durability, making it suitable for various applications beyond jewelry.
• What role does X-ray diffraction play in the identification and quantification of corundum in mineral samples?
  • X-ray diffraction is an essential technique for identifying and quantifying corundum because it provides detailed information about the crystal structure and orientation. By analyzing the resulting diffraction patterns, researchers can distinguish corundum from other minerals present in a sample based on unique peak positions and intensities. This method allows for accurate phase identification, which is crucial for understanding geological processes and mineral compositions.
• Evaluate the significance of corundum's properties in both gemology and industrial applications, particularly regarding its hardness and chemical stability.
  • Corundum's properties have profound significance in both gemology and industrial applications. In gemology, its hardness and aesthetic qualities make it highly valued for jewelry as sapphires and rubies. In industrial contexts, its hardness allows it to function effectively as an abrasive material in cutting tools and grinding wheels. Furthermore, its chemical stability ensures that it maintains its properties under varying conditions, making it reliable for use in harsh environments where durability is essential.

Related terms

Aluminum Oxide: A chemical compound consisting of aluminum and oxygen, commonly used as an abrasive and in various industrial applications.

Mohs Hardness Scale: A scale that ranks minerals based on their ability to scratch one another, ranging from talc (1) to diamond (10).

X-ray Diffraction (XRD): A technique used to identify the crystallographic structure of materials by measuring the angles and intensities of X-rays scattered by the crystal lattice.