GC1M14N What's So Tuff About Rhyolite?
Type: Earth | Size: Not chosen | Difficulty: | Terrain:
By: jp66 @ | Hide Date: 01/23/2009 | Status: Available
Country: United States | State: Colorado
Coordinates: N39° 20.494 W104° 50.486 | Last updated: 08/30/2019 | Fav points: 0

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This earthcache takes you to a developed park with a wheelchair-accessible display of Castle Rock Rhyolite.

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About 36 million years ago, there was a catastophic volcanic eruption near Mt. Princeton in the Collegiate Range, about 100 miles to the west. The eruption created a superheated cloud of pumice, ash, and rock that traveled to this area within about an hour. As it landed, it melted together under its own weight and formed a welded tuff, a glassy rock that has become known as the Castle Rock Rhyolite or Wall Mountain Tuff.

Castle Rock Rhyolite has been found throughout Douglas County, up to 20 feet thick in places. Nearby Quarry Mesa was mined for many years and the rhyolite was shipped throughout Colorado and neighboring states.

Park trails lead to the top of Quarry Mesa where you can see what is left of the original deposit. Park developers have placed some large specimens of rhyolite on display near the park entrance.

The earthcache is located at one of the rhyolite specimens. Examine the specimen and notice some of the features.

On the east side of this specimen, there is a small cavity lined with white crystals, similar to the inside of a geode. Lower down, you can see a former cavity that is completely filled with ochre-colored silica. There are also open cavities visible with no crystals. These cavities are bubbles of fluid or gases that were trapped when the rhyolite solidified.

If you look closely, you can see small specks of crystals. These were formed in the magma before it erupted and traveled downwind along with the molten ash. The tiny white needles are feldspar and the small black specks are biotite. These are the same minerals that you would find in larger crystals in Pikes Peak Granite.

This rhyolite is ideal for a building stone because of its uniformity, durability, and light weight. The glassy matrix does not have cracks that weaken many types of rock. When it does break, it breaks in conchoidal fractures similar to patterns in broken glass or other non-crystalline volcanic rock like obsidian.

To log this cache, answer the following questions in an email to the owner. Do not post the answers in your online log.
1. Estimate the size range of the cavities you can see in this specimen.
2. Estimate the size of the feldspar and biotite crystals in this specimen.

Post a photo of yourself and your GPS in front of the rock specimen.

06/07/2019 By KCCG
Will send answers later. Thanks

Pic proves our late night visit!

Kicking off the summer with a great American road trip to celebrate M4ISU’s belated birthday!  After months of planning, I am finally on the road with Stephenjha as my copilot.  I am logging as we go which makes it easier to keep track of the HUGE playlist we are hoping to accomplish.  If all goes well, I’ll drive 2500+ miles, add 50+ new counties, see 5 different states, find some cool cemeteries, increase my Fizzy and Jasmer progress, find 20+ virtuals, a handful of Earthcaches, a Wherigo, and maybe a webcam or 2!  It’s going to be a crazy weekend!  

TFTC. SL. Thanks for placing this hide for my enjoyment, I really appreciate your effort! CACHE ON!!!

06/07/2019 By Stephenjha
Second day of caching road trip to Colorado with KCCG. Spending the day covering the miles and collecting counties and interesting caches. Today is day 2632 of my daily streak. Thank you for placing this cache.

04/26/2019 By nmsunsets2
Nice break off the interstate on our way to Denver. Lovely park. The puppies enjoyed the break. Interesting earth cache. Answers sent. Thanks for the earth cache.

04/10/2019 By Dud&Plato
We had a couple of choices on what earthcache to target today, and this one looked too good to pass up. The weather did make it a bit more of a challenge, but we persisted to get friendly with some wet rhyolite. A lot of informative plaques on site, I made sure to grab photos of for review later. This is such a nice park, I have made a note to return to enjoy it more in nicer weather. For now, though, this stop added a unique bit of appreciation for rhyolite I surely wouldn't have had otherwise. Even with the wet conditions, it was a really great stop, and I'm glad we picked this earthcache. Answers have been sent to CO. TFT Earth cache and bringing us out here as well as expanding our knowledge.

04/10/2019 By BriaTeragram
Today was a busy wet and snowy day. This was icon seven of eleven for the day. When we got to the area snow had started falling. Looked all over the specimen at the coords, but had difficulty locating the area that would hold the answers to the questions. Despite circling the rhyolite, never managed to see the ochre colored silica. Not sure if the rain and snow made it more difficult or not. But I loved learning about the rocks and all their special qualities. TFTC

06/28/2018 By Scaber
I love Earth caches. Answers emailed to creator. Drove down to Castle Rock in order to get some finds for the enchanted creatures challenge. Thank you for placing this cache and helping to keep our recreation going.

06/02/2018 By the5millers
This was one of ours stops today, since we need to increase our Earthcache numbers. Thanks for this lesson of the environment. With PoshCacher and MagicCacher. Answers sent. Tftc

05/23/2018 By VeesMom
Little late in logging this cache. These were found in the course of several trips with dagrandpa. I believe he has already logged this cache. thanx for placing.

04/28/2018 By jasperdakota
Found with Nerak2001, geodog Patches and new geopuppy Riley while caching in the area. Interesting to learn about these rocks.

03/13/2018 By WindAtMyBack
Found with @LostinDenver and @intrepiidexplorer TFTC cool needles and geodes