How Rocks are formed

Igneous Rocks
Even though currently it is believed that most of the mantle right underneath the crust of the earth has been solidified, there are still a lot of areas with molten rock. When the molten rock cools and then solidifies it turns into rocks and minerals. The molten or melted area is then called magma.

 If you have ever seen a volcano, you will see that the lava that it erupts is actually magma that spills onto the surface of the earth. After the lava cools it is an igneous rock. The process in which magma is delivered to the earth is known as extrusive.

However, a much greater amount of magma has been brought to or near the surface of the earth by being forced onto other rocks where it then solidifies or hardens. The process or action is what is known as plutonic or intrusive rocks. As these rocks then cooled down and hardened, they produced a lot of the minerals and metals that the prospectors of this day and age look for.

Intrusive igneous rocks hold the interest of prospectors whereas volcanic rocks are not as significant to them. This is mainly due to the fact that igneous rocks have formed a great deal of the commercial mining deposits that have been discovered in the recent past.

Intrusive rocks are practically inserted into the open areas in the crust of the earth by pressures down under. The material on the bottom cools quickly and produces fine-grained rocks. There are times in which the intrusive rock covers parts of the undersurface of the earth for thousands of square miles and turns into country rock around the lodes that are mined. Some of the known of forms of these big deposits are syenite, periodotite, granite, and gabbro. The extrusive rock that is most commonly found is basalt, which is a country rock in a lot of mines as well.