Answer:
Minerals Available in Rock
Texture
Color
Chemical composition
Explanation:
There are different criteria that could be used to classify rocks that are igneous. These are:
1) Minerals Available in Rock: The minerals in a rock and their relative proportions in the rock mainly rely on the magma's chemical composition.
2) The Rock's texture: Rock texture largely relies on the magma's cooling history. Thus rocks with the same chemical composition and presence of the same minerals could have very distinct textures.
3) Color: A rock's color relies on the minerals and the size of the grain. Generally speaking, rocks containing lots of feldspar and quartz are light colored, and rocks containing lots of pyroxenes, olivines and amphiboles (minerals of ferromagnesium) are dark colored. But when applied to rocks of the same structure but distinct grain size, color can be misleading.
4) Chemical composition: The most distinctive characteristic is the chemical composition of igneous rocks. The structure generally represents the magma's structure, thus providing data about the rock's source.
The reason why the Midwestern United States have a very fertile soil, but Canada doesn't, despite both of them being covered by glaciers until relatively recently, and both having the same age of soil, is the climate and vegetation.
Canada is much colder than the Midwest, its winters are longer, and the summers mild, while the Midwest has higher temperatures, prolonged period of drought, and seasonal rainfall.
Because of this, Canada has been covered by coniferous forests. They leave relatively little biomass, and also the climate is making the decomposition of the biomass very slow, thus resulting in relatively poor soil quality.
In the Midwest, the climate is perfect for the development of the grasslands. The grasses grown and die each year. They live a lot of biomass, and the higher temperatures contribute that the biomass decomposes pretty quickly, thus resulting in good quality soil.
