Scientists find dense rock on earth's surface that is made of magnesium and smaller amounts of silicon. what layer of earth might the rock scientists study?

Oh the answer is the Mantle, You can look at a chart and easily find the answer if you don't believe me. But here is a reasoning; Magnesium as well as Aluminum are located within the Mantle.

From the crust or mantle
1. By studying things from Earths layers that have been pushed up through the cracks of the crust.

2.By measuring diffrent kinds of vibration from earthquakes

3.By doing laboratory expirements