Slate

LL Demos & Labs: Rock Profile: Slate, Lab: Mashed Sediment Review

This is a very flat, dark gray sample from Utah. Slate is the rock first formed as a result of increasing temperature and pressure. In rocks with a fair amount of clay (siltstone and mudstone), the minerals in the clay will start to slowly transform into mica. The clay minerals, which are flat to begin with, will turn so that the flat sides are perpendicular to the compression. This is what makes the rock so flat.