In the naked eye identification, high-quality bentonite is pure white, generally gray or light yellow-white, often light green, light blue, rose red and other colors due to water absorption or impurities. It remains pure white, gray or light yellow-white after air-drying. After breaking it by hand, the section is not flat, but it is jelly-like. It has a grease luster and feels slippery to the touch. It can absorb water and swell, and the good one can become colloid. If the water is lost after long-term air-drying, it can become loose again. Bentonite can absorb or absorb various colors because of its strong ion exchange force. Mix it with grease to make the grease more slippery. The suspension of its fine powder and water has good dispersion (dispersion) and is not easy to precipitate. The types of natural bentonite are mainly divided into calcium, sodium, hydrogen, hectorite, etc. according to the relative content of the cations of montmorillonite, among which the clay mainly composed of calcium montmorillonite is called calcium-based bentonite. Most of the bentonite mines in my country mainly produce calcium-based bentonite. Calcium-based bentonite is cheaper and easier to obtain than sodium-based bentonite. Therefore, we use calcium-based soil in the experiments of broilers and laying hens. Feed the chickens with bentonite additives, because the palatability is good and the chickens love to eat them.
However, the sensory identification such as the naked eye introduced above is not accurate enough. There is no unified national standard for the identification of bentonite in my country. Most mines implement the Ministry of Machinery's "Ministry of Standards for Bentonite and Clay for Foundry" (1997) and enterprise standards. It mainly measures the amount of blue suction, moisture, colloidal medium, passing rate, wet compressive strength, expansion coefficient, pH value, etc. The measurement methods and standards are omitted here.