10th Annual Easter Event
brought to you by guamgirl46
This cache was placed as part of the 10th Annual “Put on Your Easter Bonnet - A Multi-Cache Event” held each Spring. To attend, check geocaching.com for new Guam caches or join the Guam Geocachers’ Facebook page.
If you enjoyed this cache, please consider awarding it a Favorite Point.
Geocache Description:
~ An Earthcache is a “special place that people can visit to learn about a unique geoscience feature or aspect of our Earth . . . Visitors to Earthcaches can see how our planet has been shaped by geological processes, how we manage the resources and how scientists gather evidence to learn about the Earth.”
~ Please read the cache page to assure you have what you need to verify your answers.
Today’s, focus is Vesicular Basalt. As you look at the nearby roadcut, you will be trying to answer the following questions:
1. How would you describe the Texture? Is it fine or rough to the touch? What caused it to have that texture?
2. How would you describe the color? Is it light grey, dark grey, or black? Why do you think it is this color?
3. Attach a picture of an example of the Vesicular Basalt you are viewing.
Rocks are grouped into three categories: igneous rocks, sedimentary rocks and metamorphic rocks. Igneous rocks are formed when magma cools in the Earth's crust, or lava cools on the ground surface or the seabed. Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock is subjected to temperatures greater than 300 to 400 °F and, often, elevated pressure of 100 megapascals or more, causing extreme physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition.
Vesicular Basalt is an igneous rock and is classified according to its texture and composition. Texture refers to the size and arrangement of the minerals or grains that make up a rock, the visual or tactile surface characteristics and appearance. Composition refers to both the types of minerals within a rock and the overall chemical makeup of the rock, the general makeup of the rock.
Basalt is one of the most common rock types on Earth. It can be found in various locations around the world, both on land and under the ocean floor. It is a type of volcanic rock that is formed from the solidification of molten lava. It is an igneous rock, having been formed through the cooling and solidification of magma or lava.
Vesicular basalt
Vesicular basalt comes from lava flows. It is a black rock that contains many small round holes. These holes are known as vesicles. They come from gases that were trapped in the lava. If the bubbles do not get large enough to pop, they are frozen in the lava as vesicles, looking somewhat like Swiss cheese. This rock tends to weather easily to a green or gray rock, not as dark as fresh basalt.
Oceanic crust forms at mid-ocean ridges, where plate tectonics are in the act of tearing the Earth’s surface apart. As tectonic plates (plate tectonics is a scientific theory that explains how major landforms are created because of Earth's subterranean movements) break away from each other, material from the mantle, made molten by the sudden reduction in pressure, bubbles up to fill the void and crystallizes to form new crust. Over time these rocks get covered in marine sediments, composed of the finest mud and hundreds of meters of nannofossil ooze, forming the ocean floor as we know it today.
Vesicular basalt is an igneous rock. It has a fine-grained texture and is known for its dark color, typically ranging from black to dark gray.
While basalt can have a range of compositions, it is typically rich in iron and magnesium, and low in silica. It is composed mostly of minerals such as pyroxene, plagioclase feldspar, and sometimes olivine.
To Log this Earthcache, please send your responses to the questions listed above to the Cache Owner’s profile listed at the top of this page. Do Not include your answers in your online log.
Please don’t be intimidated about answering the questions. They are meant to improve your understanding of the geological aspects of the earth and provide you with some new knowledge and/or insights about the characteristics what we find here on Guam. You don't have to write a term paper. Just provide enough information to show me that you were there and tried to understand the basics about Vesicular Basalt. But, most importantly have fun. I hope you take away some new knowledge with a smile on your face.
Resources:
American Geophysical Union – September 8, 2014 edition
Britannica
Department of Geology & Planetary Science
ROCKS and MINERALS of GUAM: A Guide to Identifying What You Find Around our Island by Brenna Lorenz
Minerals, National Park Service
The ‘hole’ story about vesicular basalt - Oct 2022