The lower layer of the mantle is composed primarily of silicate minerals, specifically bridgmanite and ferropericlase. These minerals are very dense and are formed under the intense pressure and temperature found in the lower mantle.

Here's a breakdown:

* Bridgmanite: This is the most abundant mineral in the Earth's lower mantle, making up around 70%. It's a silicate mineral with a complex crystal structure that can withstand the extreme pressure and temperature.

* Ferropericlase: This is another important mineral in the lower mantle, composed of iron and magnesium oxide. It's also very dense and plays a significant role in the Earth's magnetic field.

In addition to these two main minerals, the lower mantle also contains smaller amounts of other minerals like wadsleyite, ringwoodite, and calcium silicate perovskite.

It's important to note that directly studying the lower mantle is extremely difficult due to its depth and inaccessibility. However, scientists use various techniques like seismic wave analysis and laboratory experiments to understand the composition and behavior of the Earth's interior.