Inside Mullite / PART 1: What It Is and Why It Matters
Built for Extremes
Mullite is a powerhouse in the ceramics and refractory industries—and for good reason. Known for its low thermal expansion, thermal shock resistance, and resistance to chemical attack, it thrives in high-temperature, high-stress environments. Whether it’s withstanding the intense heat of a foundry or enduring the harsh demands of aerospace applications, mullite performs where other materials fail.
A Rare Find in Nature
Despite its industrial importance, mullite is rarely found in nature. It forms only under high-temperature, low-pressure conditions—an unusual combination on Earth. The first documented discovery came in the 1920s, when Bowen and Grieg identified the mineral in lava flows on the Isle of Mull in Scotland. There, clay-rich sediments had fused with magma, creating a new aluminosilicate with a 3:2 alumina-to-silica ratio. That find gave mullite its name, but because naturally occurring deposits are so scarce, all industrial mullite today is produced synthetically.
What is Virginia Mullite?
That brings us to Virginia Mullite®. Produced by calcining refined kyanite at over 1450°C, Virginia Mullite is engineered for performance. It contains approximately 80% mullite, 11% finely dispersed amorphous silica, 7% quartz, and trace amounts of cristobalite. This unique combination results in a highly stable, high-purity material that delivers reliable performance in extreme conditions.
What Sets it Apart?
What sets Virginia Mullite apart is how it's made—and what that means for performance. We put a lot of effort into creating the highest quality kyanite possible through numerous processing steps. This purity is maintained after calcination into Virginia Mullite. The impurities found in Virginia Mullite are among the lowest in the industry, with low levels of iron oxide, titania, and alkalis. This gives Virginia Mullite excellent hot properties, including creep resistance. Additionally, Virginia Mullite retains the blade-like (acicular) crystal shape of kyanite after calcination, unique for mullite aggregates, which promotes strength at high temperatures.
Mullite vs. Kyanite
Both mullite and kyanite are important refractory materials—but they serve different purposes. Kyanite expands during firing, helping to offset shrinkage in a mix. Mullite, by contrast, offers exceptional volume stability and imparts important thermal, physical, and chemical properties to the mix. While kyanite is often used as a supporting additive, mullite is used in greater volumes—especially in applications where resistance to thermal shock and chemical attack are critical to performance.
Ready to Optimize Your Refractory Mix?
If you’re looking to strengthen your refractory mix or improve thermal stability, we’re here to help. Reach out to start the conversation:
Email: sales@kyanite.com / Phone: +1 (434) 983-2043
Up Next: Stay tuned for Parts 2 and 3 of our Inside Mullite series, where we’ll take a closer look at how Virginia Mullite is made—and the industries that depend on it every day.
