In The Essence of Zisha (Part I): An Exploration of Yixing Teapot Permeability, we explored porosity. In Part II: Unmasking the “Da Hong Pao” (Big Red Robe) Clay Myth, we uncovered the truth about “Da Hong Pao”. Today, we look at the microscopic level: The Mineral Composition.
A common rule of thumb in the industry is: “The redder the clay, the higher the iron content.” But is it that simple?
Based on data published by the China University of Geosciences (using X-ray diffraction analysis), we can now visualize exactly what makes Zhuni red and what creates the unique texture of Di Cao Qing.
Key Takeaways: The Mineral Secrets
- Color Source: The redder the clay, the higher the iron content.
- The Iron Difference: Zhuni relies on Goethite (针铁矿), while Zini relies on Hematite (赤铁矿).
- Gloss & Shrinkage: High content of Illite and Montmorillonite leads to higher shrinkage but better “water color” (glossiness).
- The “Gold Specks” Mystery: Di Cao Qing is unique for containing Pyrophyllite, which likely creates its signature “white/gold specks” or “chicken eyes.”
1. The General Composition: Iron Determines the Color
The following table shows the breakdown of minerals in various Yixing ores. The key finding here is that the type of iron matters more than just the amount.
| Ore Type (Origin) | Quartz (石英) |
Clay Minerals | Hematite (赤铁矿) |
Goethite (针铁矿) |
Feldspar Group |
|---|---|---|---|---|---|
| Di Cao Qing (底槽清) | 28.9% | 62.6% | 7.4% | – | 1.1% |
| Zini (Purple Clay) | 44.5% | 46.6% | 8.0% | – | 0.9% |
| Zhuni (Zhao Zhuang) | 37.6% | 47.1% | – | 13.6% | 1.7% |
| Zhuni (Xiao Mei Yao) | 39.1% | 48.0% | – | 10.4% | 2.5% |
| Zhuni (Huanglong Shan) | 42.4% | 38.7% | – | 16.7% | 1.2% |
| Lvni (Green Clay) | 29.5% | 67.8% | 1.0% | – | 1.7% |
| Duanni (Huanglong Shan) | 45.5% | 46.9% | 0.8% | – | 1.5% |
| Red/Green Symbiotic | 36.9% | 50.1% | – | 11.1% | 1.9% |
💡 Analysis: Goethite vs. Hematite
From the data above, we can draw a definitive conclusion about Yixing colors:
- Zhuni (Vermilion Clay) relies on Goethite: Unlike other clays, Zhuni contains a high concentration of Goethite (针铁矿), ranging from 10.4% to 16.7%. This specific iron mineral is what gives Zhuni its vibrant, orangey-red hue.
- Zini (Purple Clay) relies on Hematite: Zini and Di Cao Qing contain Hematite (赤铁矿) in the range of 7.4% – 8.0%. This results in the deeper, purplish-brown tones.
- Lvni (Green Clay) is Iron-Poor: With only roughly 1.0% Hematite, Lvni lacks the red pigment, resulting in a yellow/green firing color.
2. Clay Minerals: The Secret to “Water Color” & Shrinkage
The term “Clay Minerals” in the first table refers to a mix of complex minerals. The table below breaks these down further. These minerals determine how much the pot shrinks and how glossy (“Shui Se” / Water Color) it becomes.
| Ore Type | Pyrophyllite (叶腊石) |
Kaolinite (高岭石) |
Illite (伊利石) |
Montmorillonite (蒙脱石) |
Firing Shrinkage |
|---|---|---|---|---|---|
| Di Cao Qing | 64% | 27% | 5% | 4% | 3% |
| Zini | – | 95% | 5% | – | 5% |
| Zhuni (Zhao Zhuang) | – | 16% | 84% | – | 8.6% |
| Zhuni (Xiao Mei Yao) | – | 5% | 60% | 35% | 8.5% |
| Zhuni (Huanglong Shan) | – | 3% | 90% | 7% | 9.57% |
| Lvni | – | 57% | 33% | 10% | 8.16% |
| Duanni (Huanglong Shan) | – | 79% | 21% | – | 6.19% |
| Red/Green Symbiotic | – | 39% | 59% | 2% | 8.7% |
💡 Analysis: The “Gloss” Factor
Looking at the data, we see that Illite and Montmorillonite play a huge role in Zhuni.
- The higher the content of these two minerals, the higher the shrinkage rate (creating the famous Zhuni wrinkles).
- However, they also contribute to a better “Shui Se” (Water Color), giving the pot a natural, oily gloss without any polishing.
3. The Di Cao Qing Mystery: What are the “White Specks”?
One of the most unique findings in this study is the composition of Di Cao Qing (底槽清).
It is the only clay in the list containing Pyrophyllite (叶腊石)—and it contains a massive 64%.
- The Science: Pyrophyllite (Al₂Si₄O₁₀(OH)₂) is an aluminum silicate compound known for high heat resistance. It fully transforms into anhydrous pyrophyllite at around 1200°C.
- The Connection: 1200°C is the typical firing temperature for Di Cao Qing.
- The Conclusion: The famous “Gold Specks”, “White Particles”, or “Chicken Eyes” (鸡眼) visible on authentic Di Cao Qing teapots are highly likely to be these Pyrophyllite crystals.
This scientific proof validates the traditional method of identifying authentic Di Cao Qing by looking for these faint particles.
Conclusion
Zisha is complex. It is a natural mixture of quartz, clay minerals, and iron ores.
- Zhuni is red because of Goethite.
- Zini is purple because of Hematite.
- Di Cao Qing is unique because of Pyrophyllite (the “white specks”).
While understanding the chemical formula won’t necessarily change the taste of your tea, it helps us appreciate that Yixing Teapots are not just art—they are geology in your hands.
Experience the Difference of Real Mineral Clay
You’ve learned about the Goethite in Zhuni and the Pyrophyllite in Di Cao Qing. Now, experience how these minerals interact with your tea. At Fong’s Tea, we prioritize authentic, original ore (Yuan Kuang) over marketing gimmicks.
FAQs
According to X-ray diffraction analysis, Zhuni (Vermilion Clay) contains Goethite (针铁矿) as its primary iron source (10-16%), while Zini (Purple Clay) contains Hematite (赤铁矿) (7-8%). This difference dictates their firing colors.
Geological studies indicate that Di Cao Qing contains approximately 64% Pyrophyllite (叶腊石), a mineral that withstands high temperatures. These crystals are likely the source of the “white specks” or “chicken eyes” seen on the teapot’s surface.
Zhuni typically has the highest shrinkage rate (around 8.5% to 9.5% or higher depending on temperature). This is linked to its high content of Illite and Montmorillonite clay minerals.
