Igneous Rocks
The first rocks were igneous rocks, formed over 4.5 billion years ago as magma cooled and formed the earth's crust. Their name comes from the Latin word ignis, which means fire. There are two kinds of igneous rocks.
Extrusive igneous rocks form when magma reaches the earth's surface, typically through a volcano. The magma cools quickly and the minerals are very fine in crystal structure. Obsidian (volcanic glass) and pumice are typical extrusive igneous rocks. Volcanic ash is another extrusive igneous rock, and it is found in many Kansas counties. All extrusive igneous rocks found in Kansas were brought here by wind, water, or glaciers. There have been no volcanoes in Kansas since the beginning of Paleozoic time, over 590 million years ago.
These are also called igneous-volcanic rocks.
Extrusive igneous rocks form when magma reaches the earth's surface, typically through a volcano. The magma cools quickly and the minerals are very fine in crystal structure. Obsidian (volcanic glass) and pumice are typical extrusive igneous rocks. Volcanic ash is another extrusive igneous rock, and it is found in many Kansas counties. All extrusive igneous rocks found in Kansas were brought here by wind, water, or glaciers. There have been no volcanoes in Kansas since the beginning of Paleozoic time, over 590 million years ago.
These are also called igneous-volcanic rocks.
Intrusive igneous rocks form when magma cools within the earth's crust. It cools slowly, so the minerals in the rocks are usually larger crystals. Erosion may later expose these intrusive igneous rocks. One of the most common igneous intrusive rocks is granite.
There are seven known localities in Kansas where erosion has exposed native igneous rocks: the Silver Dome and Rose Dome in Woodson County and five locations in Riley County. At these locations, we find lamproite, granite, and kimberlite.
Igneous intrusive rocks can be collected in other places in Kansas, but they have been carried in by water or glaciers and are not native.
These are also called igneous-plutonic rocks.