Week 2 - Igneous Rocks - Ryan Klassy

Igneous rocks used for important cultural reasons.

Last year, my wife and I traveled to Osaka, Japan to have our wedding. We had been married 10 years already, but we never did a ceremony back then, we just did the paperwork. This was a trip for us to have a small ceremony in our favorite place in the world; Japan.

We had been to Tokyo a few times in the past, but this time we went to Osaka. During our week in Osaka, we decided to take a day trip on the train to Kyoto and Nara which are both about an hour train ride away. Half way between Osaka and Nara are the Ikoma Mountains.

The Ikoma Mountains are a mountain range that stretches from north to south and is situated just east of Osaka. There are many different areas of this mountain range that are very geologically diverse. Some portions on the lower elevation areas are mostly sedimentary, while many of the highest peaks contain some metamorphic rock. The majority, however, is made up of igneous rock.

Beautiful traditional usage shows the importance of rock.

The area we visited on our way to Nara was the Kyukakurin Temple and it's surrounding trails. This area is primarily formed by intrusive igneous rock. The intrusive igneous rock differs from the extrusive igneous rock in the location/environment in which it was formed. The intrusive igneous rocks are formed deep under ground where temperatures and pressures are high. The rock is formed from what is called a parent magma. These underground collections of magma contain many different minerals which slowly cool as their heat is dissipated into the cooler surrounding crust. As the magma cools, mineral crystals begin to form. In the particular area where we visited, the rocks were mainly granite, but there were also signs of gabbro.

Both granite and gabbro are intrusive igneous rocks, but they differ in their mineral compositions. Granite is a rock formed from felsic magma. Felsic magma tends to have a higher silica content, less iron/magnesium/calcium (nonferromagnesian), tend to be lighter in color and has a lower melting point. Gabbro, on the other hand, is a mafic rock which contains less silica, more iron/magnesium/calcium (ferromagnesian), tends to be darker in color and has a higher melting point.

You can see from the pictures of the shrine that the exposed rock is a light colored granite. The photos are not close enough to see particle size and details, but a geological survey map of the area indicates that the exposed rock is in fact granite.

Notice the weathering of the igneous rock.

You can see that weathering has really taken a toll on the exposed areas, although it is mostly the sedimentary rocks which have been carved away over time, leaving these large exposed granite rocks.

When I visited this area, I did not know the slightest thing about rock formations. Now after only one week studying the igneous rocks and the rock cycle, I feel substantially more confident about them! I would absolutely love to re-visit some of the many locations I have been to in the past to really look at them in this new light. It is so exciting to me to get into a new branch of study like this because it opens my eyes to the details of the world around me.

Granite Region Details

Gabbro Region Details