Tea leaves are often adulterated with chemicals and additives that add to its aroma or flavor. But the most common kind is color. Take a filter paper and spread a few tea leaves on it. Sprinkle some water over the filter. If there is any color present in the leaves then it will stain the paper. Now wash the filter paper under tap water and carefully look for stains against the light.
Iron fillings: Hold magnet over tea powder and iron will attach to magnet
Iron fillings: Spread coffee powder on a paper and slowly move magnet on the powder -if there is iron contamination then iron powder sticks to magnet
Chicory: Eventhough chicory is considered as accepted adulterant, many countries does not allow chicory in coffee. Ground chicory when thrown on cold water sinks quickly, coloring the water, and is soon softened, whereas ground roasted coffee floats, imparting no color. Chicory is easily bleached by chlorinated soda (labarraque solution); coffee is but slowly affected by this bleaching agent.
Image from: https://www.youtube.com/watch?v=rVQB-rvWj3I