Is our topic
Solid until hit
Then wobbles quite a bit
This is not a very good definition, so for more on thixotropy you can start with the Wikipedia article, which should give you the information you need for proper research. I believe I first came across the word in a crime thriller called Landslide!; as everyone knows any book with an exclamation in the title is bound to be quality. Number 177.
 Checking the internet suggests that I may have recalled the title wrong as it is listed without the exclamation mark. Since I think the cover had a bloke shouting on it with title where a word balloon ought to be, I may have mentally inserted it as a warning. Need I note that the title is a spoiler?