Cascarilla reminds by taste an industrial chalk. It tastes like a white soft earth with a bit of chemical aftertaste. It is not really for eating, but I understood that some practicioners sometimes put it on the lips and tongue, and after it gets swallowed.
Below is some more information from internet, and what we heard around:
It comes from the traditions of west Africa. Like other beliefs people brought to the concept of eating sacred white earth and called it efun. They belief that it can protect them against evil. They were looking for alternative earth which have the same effects and that’s where the cascarilla powder comes from. it was already known by Caribbean natives they used it for medicinal properties. Also, it has a white color like the efun. Over time, Santeria practitioners transitioned from using this powder to using crushed egg shells. These were easier to get, and the symbolism of the life-giving egg also made it attractive.