The Odd Boulder
This Earthcache is located in Cypress, Texas. Since it is an Earthcache, there is no physical container to find. To earn a smiley for the cache, e-mail or message the cache owner your answers to the questions BEFORE you log a find.
We have heard the phrase “odd duck” many times. The odd duck refers to a person with a quirky personality or unusual habits. This Earthcache will provide you with a unique experience and you will learn more about a type of rock. At GZ, there are six boulders. Which one do you think is the Odd Boulder?
Human-Environmental Interaction
In geography, five themes can be used to classify how we view the world. One of these themes is Human-Environmental interactions, which can be thought of as how humans have modified or altered the environment. Hundreds of acres of Blackland Prairie in Northwest Harris County have been bulldozed to create roads, businesses, and homes.
As you drive near GZ, you will observe several large boulders placed throughout the landscape – along sidewalks and homes. Why these large-looking boulders?
Landscapers and home designers have chosen sandstone boulders as decoration. However, we can ask ourselves why. Sandstone doesn’t decompose or erode very fast. Thus, it will be around for many, many years. In addition, because of the hot and humid conditions of Southeast Texas, sandstone boulders are not prone to fungus or algae growth.
Sandstone v. Mudstone
How is sandstone formed and what is the difference to mudstone? Sandstone is a rock primarily made of minerals derived from sand and is formed over hundreds of years by lake and river deposits.
Conversely, mudstone comprises tiny clay particles created in tidal flats, lakes, and deep seas.
How Old is the Sandstone
How did the area then get sandstone for decoration? During the Cenozoic Era, deltas, fed by northern rivers, were formed along the present-day Texas Coast. Late in the Cenozoic Era, the Ice Age occurred. While Texas did not see thick sheets of ice, the Gulf Coast did drop approximately 300 to 450 feet. As rivers flowed through this area, it carried more water and sand to the sea.
The Wilcox comprises the oldest and thickest sandstone deposited 2.6 to 66 million years ago along the present-day Texas Gulf Coast. It crops out in a band between 10 and 20 miles wide, approximately 100 to 200 miles inland from the Gulf of Mexico. Large river deltas deposited the sand that formed the Wilcox Sandstone Formation.
The boulders at GZ were chosen for their visual appeal and proximity to the Salado Sandstone Quarry in Central Texas.
Layers of a Cake
The Wilcox sandstone was once on the surface of the Gulf Coast of Texas millions of years ago. However, over time, other dirt, mud, and debris fell onto the surface, burring the sand and forming sandstone. As these layers of the Earth’s cake piled onto the sand, pressure fractured portions of the sandstone over time.
In these fractures flowed silica-rich water. As the pressure of the layers pushed down on the fractures, the temperatures rose. The high temperature allowed the silicon dioxide to dissolve, like sugar in hot tea. As the temperatures dropped, the solution became saturated, forming quartz crystals.
Quartz is a common mineral made of oxygen and silicon. Quartz crystals can be either Crystalline or Cryptocrystalline. Crystalline quartz is found as tiny crystals sparkling on a rock surface in various colors. Cryptocrystalline quartz does not form visible crystals.
Igneous, Metamorphic, Sedimentary
Igneous rocks are formed from melted rock deep inside the Earth, whereas sedimentary rocks are formed from layers of sand, silt, and dead plants and animals. Metamorphic rocks are formed from other rocks that are changed by heat and pressure underground.
After reading the information above and observing the object at GZ, please answer the following questions:
- Observe and describe the texture and color on the top of the Odd Boulder.
- Look closely at the top of the Odd Boulder – what do you see in the corners? Based on your observation, what type of crystal do you think it is?
- What size and color are the crystals?
- Size: basketball, softball, baseball, golf ball, marble or pin
- Do you think the Odd Boulder is Igneous, Metamorphic, or Sedimentary? What did you observe to make your conclusion?
- Take a picture at GZ with one of the two sandstone boulders in the background. DO NOT POST PICTURES of the ODD BOULDER.
Bonus question (not required, but helpful): If you are looking west at GZ, what rock type do you think is to the left of the Odd Boulder?
Confirm your findings by answering these questions and sending
Your answers via the message center.
**Do Not post answers in your log**
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References:
Geologyscience, 2024. Sandstone. Geologyscience.com https://geologyscience.com/rocks/sandstone/#:
King, Hobart M. 2024. Sandstone. Geology.com. https://geology.com/rocks/sandstone.shtml
Rice, Addison. 2024. How Does Quartz Form? International Gem Society. https://www.gemsociety.org/article/how-does-quartz-form/