الألومينا أحادية البلورية, و غالبا يشار له لها ب “الألومينا الكريستالية المفردة” أو ببساطة “الياقوت” في بعض السياقات, هو نوع من الألومينا (Al₂O₃) التي لديها واحدة, continuous crystal structure. This is in contrast to polycrystalline materials, which are made up of numerous small crystalline regions or grains with different orientations.

Monocrystalline الألومينا exhibits unique properties due to its singular crystal structure, مشتمل:

1. Optical clarity: Monocrystalline alumina is transparent in its pure form and can transmit light over a wide range of wavelengths, from ultraviolet to infrared. This makes it useful for applications like sapphire windows and watch crystals.
2. صلابة عالية: Sapphire ranks 9 on the Mohs scale of mineral hardness, making it one of the hardest known materials, surpassed only by diamond.
3. الاستقرار الحراري: Monocrystalline alumina has a high melting point and maintains its strength at high temperatures.
4. مقاومة كيميائية: Sapphire is chemically inert and doesn’t react with most acids, قواعد, and other chemical agents.
5. Electrical insulating properties: Monocrystalline alumina is an excellent electrical insulator.

بسبب هذه الخصائص, monocrystalline alumina finds application in various fields, مشتمل:

• إلكترونيات: Substrates for some semiconductor devices.
• Optics: Windows, lenses, and optical components, especially in harsh environments.
• Watch industry: Scratch-resistant watch faces.
• Medical: Surgical tools and endoscope optics.

The method commonly used to produce large single crystals of sapphire is known as the Kyropoulos method or other bulk crystal growth techniques.