Skip to main content

Geodes How to Guide

Geodes (derived from a Greek word meaning "Earth-like") Geodes are geologic secondary formations within sedimentary and volcanic rocks. Geodes are hollow, somewhat circular or rounded rocks, in which masses of mineral matter (which may include crystals) are hidden inside. The crystals typically pointing inward are formed by the filling of pitted or hollow cavities in volcanic and sub-volcanic rocks by minerals deposited from hydrothermal fluids; or by the dissolution concretions formed at the same time as the enclosing rock and partial filling by the same, or other, minerals precipitated from water, groundwater or hydrothermal fluids.  
Some will call any round rock a geode, while others insist it must be hollow, this doesn’t always hold true because the filling of cavities is a process that normally continues to completion. So just before that last amount of void is filled it is still a geode, then suddenly it is not a geode it becomes a nodule or a Thunder Egg.

Examples of Geode types

The inside of a large geode can be lined by Amethyst crystals, or many other types of crystals or drusy.

More than rock can become Geodized , an example is of a Brachiopod fossil lined with calcitewith a single crystal of sphalerite, from the Devonian of Wisconsin.

Formation                                                                                                                                Geodes can form in any cavity, but the term is usually reserved for rounded formations in igneous and sedimentary rocks.  They can form in gas bubbles of inigneous rocks, such as vesicles in basaltic lava; or, as in the American Midwest, in rounded cavities in sedimentary formations. After rock around the cavity hardens, dissolved silicates and/or carbonates are deposited on the inside surface. Over time, this slow feed of mineral constituents from groundwater or hydrothermal solutions allows crystals to form inside the hollow chamber. Bedrock containing geodes eventually weathers and decomposes, leaving them present at the surface if they are composed of resistant material such as quartz.
When cut in half, visible bands corresponding to varied stages of precipitation may at times show patterns that reveal points of fluid entry into the cavity and/or varied colors corresponding to changes in chemistry.
Three separate occurrences have been formulated. 1. Gas bubbles filling the void and then a secondary mineral fills the void, 2. Crystals that form by volcanic action, and 3. Mineral filled voids in sedimentary strata. Part of the confusion is because the three separate kinds of voids are all basically filled the same way. Ground fluids enter the voids and depending upon the temperature and content leave deposits on all surfaces or the floors if gravity can overcome temperature induced kinetic energy.  Sedimentary voids created by earth shifts, falling rocks, voids left by dissolving minerals, or cavities left by dead creatures. Usually body oils bind clay to protect fossils. Here somehow apparently silica was attracted instead.

Vugs and Crystal cavity’s
In 2000 a team of geologists found a cave filled with giant gypsum crystals in an abandoned silver mine near Almeria, Spain. The cavity, which measures 1.8 × 1.7 meters and is 8 meters in length, would be the largest crystal cave ever found. The entrance of the cave has been blocked by five tons of rocks and is under police protection (to prevent looters from entering). According to geological models, the cave was formed during the Messinian Salinity crisis 6 million years ago, when the Mediterranean Sea evaporated and left thick layers of salt sediment). The cave is currently not accessible to tourists.
The world's largest known crystal cave or vug is Crystal cave, a celestine geode 35 feet (10.7 m) in diameter at its widest point, located near the village of Put-in Bay, Ohio, on South Bass Island in Lake Erie.

Coloration



Geode banding and coloration is the result of variable impurities. Iron oxides will impart rust hues to siliceous solutions, such as the commonly observed iron-stained quartz. Most geodes contain clear quartz crystals, while others have purple amethyst crystals. Still others can have agate, chalcedony, or jasper banding or crystals such as calcite, dolomite, celestite, etc. There is pretty much no way of telling what the inside of a geode holds until it is cut open or broken apart. However, geodes from an area are usually similar in appearance.
Geodes and geode slices are sometimes dyed with artificial colors. Samples of geodes with unusual colors or highly unlikely formations have usually been synthetically altered.


Fluorite and calcite on quartz stalactites, in geode
·         Locations                                                                                                                                Geodes are common in some formations in the United States (mainly California, Indiana, Iowa, Missouri, western Illinois, Kentucky, and Utah). They also are found in Brazil, Namibia, and Mexico, Geodes are also found in Mendip Hills in Somerset, England, where they are known locally as "potato stones".  Geode sizes range from 1 to 18 inches in diameter. Finding Geodes is hard work and you can hand crack them or cut them open to show the natural geological beauty inside these mysterious natural wonders. Hidden inside include fractal Quartz crystals, white Chalcedony, red chalcedony, blue chalcedony, Baryte minerals, Citrine, and various other favorite gems. Every cracked Geode is truly unique, collectible, and a wonder.

Noteworthy locations
Dugway Geode beds located Dugway pass, Utah. USA
Indiana Geodes. Indiana, USA.
Dryhead Agate Mine, Bighorn River area, Pryor Mts, Carbon Co., Montana, USA
Hauser Geode beds, Wiley’s Well, Ca USA.

Hunting Geodes
Geode sizes typically range from 1 to 18 inches in diameter. Finding Geodes can be hard work. Be safe use Eye protection and gloves at a minimum. Never dig into side of a hill were an overhead collapse could happen, a deceivingly small amount of just a couple inches of overhang has broken off and killed experienced geode hunters many times. Also don’t dig in areas off limits, check first, a local rock and lapidary club will often know what areas are open, and often have access to areas that the general public doesn’t, memberships are usually low and run from 30 to 60 dollars a year for a person or family. Once you locate the geode bed, dig them out of hard rock seams or sometimes in soft pot ash or gravel depending on the areas.  You can cut them with a rock saw or just hand crack them to show the natural geological beauty inside these mysterious natural wonders. Hidden inside include fractal Quartz crystals, white Chalcedony, red chalcedony, blue chalcedony, Baryte minerals, Citrine, and various other favorite gems. Every cracked Geode is truly unique, collectible, and a wonder.
Please feel free to contact me if you have anything you would like to see added here. Thank you
Shane at Radical Rocks

Check out the podcast at https://anchor.fm/shane495   Radical Rocks can be found on most podcast apps. Links below


Geodes Book https://amzn.to/2SOgnm1


Geode Kit Crack Geodes open and see whats inside! https://amzn.to/2vQl6KR

https://anchor.fm/radicalrocks
https://radicalrocksusa.blogspot.com/
MeWe, better than Facebook; https://mewe.com/join/radicalrocks
https://www.linkedin.com/in/shane-ripley-a281768/
https://www.youtube.com/channel/UCBe_Ds0ARJ7nA1TqgucZamw?view_as=public

References
1.    ^ Jump up to: a b "Geodes: The rocks with a crystal surprise inside!". geology.com. Retrieved 2017-12-30.
2.    ^ "Geodes". geology.com.
3.    ^ "The Quarries". Dulcote, Somerset. Retrieved 2017-12-30.
4.    ^ Amos, Jonathan (12 June 2000). "Giant Crystal Cave Discovered". BBC. Retrieved 3 September 2011.
5.    Oxford Dictionary of Earth Sciences pp 238-9
Further reading
- Webster's Ninth New Collegiate Dictionary p 513
Labels:

Comments

Post a Comment

Thank you for your comment. I will review content for spam and such.

Popular posts from this blog

Hauser Geode Beds, Wiley’s Well District How to Guide

Hauser Geode Beds in the Wiley’s Well District One of my first rockhounding field trips was with the Orange Belt Mineralogist Society (OBMS) This group has one of the longest history’s and ties to the discovery of the Hauser Beds. Joel F Hauser is credited with finding the Geode beds that bear his name today about 1934. Joel Hauser was also a member of the OBMS. (pictured below) This is a main reason that the OBMS was famous for leading the Wiley’s Well Thanksgiving rockhounding trips for many decades. Lately other clubs have also leading the yearly events, including the San Diego Searchers. My Son Zack and I would spend a week to 10 days dry camping, we were about as crusty as the rocks we were collecting, but it's always worth it. Camping out under the desert stars so bight you can touch them and truly see the shapes of the zodiacs. Gathering around the fire at the end of a tiring day of rockhounding telling and swapping stories of rocks and gems and old timers above. It’s t
Post a Comment
Read more

Identifying Gemstones

                                      Identifying Gemstones                                                     Close-up of Pink Crystals Gemstone identification can be tricky. Especially if you are a novice in this area, you will have a hard time figuring out what gemstone you are looking at without relying on some help. However, if you are really passionate about your gemstones then there are ways that you can learn to identify gemstones. It will take a lot of practice and some serious mental training, and the truth is that with so many different gemstones out there, the learning process never really ends. So how is it that some people learn how to identify gemstones just by looking at them? Close-up of the Amethyst Stone                  The Process of Gemstone Identification If you’ve ever tried to identify gemstones or even looked at someone trying to identify them, you are probably already aware that identifying gems is a process of finding clues and
Post a Comment
Read more

An Introduction to Lapidary Arts, Cabochon Shaping & Carving

  An Introduction to Lapidary Arts, Cabochon Shaping & Carving   Amethyst   The art of working with stones is called lapidary. However, it generally refers to small objects that were created using gem materials. So bigger ornaments or life-sized statues that were created with stones would not come under the wing of lapidary arts. Lapidary art is divided into four basic types: ·          Tumbling ·          Cabbing ·          Faceting ·          Carving However, lapidaries can be further divided into many other kinds. Some gem cutters treat it as a hobby, and are content with making basic ornaments as birthday and holiday presents for their friends and families, while others like to indulge in creating more intricate cuts and designs. Some people like to work only with the stones that they’ve found themselves. And of course, there are some serious gem cutters who may use it as a means of earning profit as well. Yet, the one thing that is common among all of the
Post a Comment
Read more