High-quality bentonite is pure white to the naked eye, though it can also be gray or light yellowish-white. It often appears pale green, pale blue, or rose-red due to water absorption or impurities. After air drying, it remains pure white, gray, or light yellowish-white. When broken by hand, the cross-section is uneven and has a gel-like texture. It has an oily luster and feels slippery to the touch. It can absorb water and swell, and good quality bentonite can become colloidal. After long-term air drying and moisture loss, it can become loose again. Because of its strong ion exchange capacity, bentonite can adsorb or absorb various colors. Mixing it with oils makes the oils more slippery. Its fine powder, when suspended in water, disperses very well and does not easily settle. Natural bentonite types are mainly classified according to the relative content of montmorillonite cations, such as calcium, sodium, hydrogen, and lithium montmorillonite. Clay with calcium montmorillonite as the main component is called calcium-based bentonite. Most bentonite mines in my country primarily produce calcium-based bentonite, which is cheaper and more readily available than sodium-based bentonite. Therefore, we use calcium-based bentonite in our broiler and layer chicken experiments. Chickens readily consume bentonite as a feed additive because of its good palatability.
However, relying solely on sensory evaluation methods such as visual inspection is insufficient for accuracy. my country currently lacks a unified national standard for bentonite identification. Most mines adhere to the Ministry of Machinery Industry's "Ministry Standard for Bentonite and Clay for Foundry" (1997) and enterprise standards. The main parameters measured include bluing absorption, moisture content, colloidal properties, throughput, wet compressive strength, expansion coefficient, and pH value. The specific methods and standards for these measurements are omitted here.
