The Earth's mantle-plasticity

In science class we are reviewing earth science from sixth grade. To help us understand why the earths tectonic plates are able to move on the mantle our science teacher set up an experiment. The experiment was a huge mess but now the earths mantle is easy to understand. My conclusion for the experiment was that: The mixture was a solid, it was like a rubber ball, but when pressure and heat was not applied the mixture turned into a liquid. When in liquid form the liquid felt like melted rubber. This mixture was not a liquid or a solid I believe it should have it's own group. When I pushed my finger into the mixture fast it quickly turned into a solid then back into a liquid. When i pushed my finger in slower the mixture stayed a solid longer. This mixture is similar to the earth's mantle because both have plasticity, meaning it is not a liquid nor a solid.