Other Free Encyclopedias » Science Encyclopedia » Science & Philosophy: Gastrula to Glow discharge


rock geodes shell crystals

Geodes are hollow rock masses that are lined with crystals that have grown toward the center of the cavity. Geodes are usually roughly spherical in shape, up to 12 A blue geode. © Royalty-Free/Corbis. Reproduced by permission.
in (30 cm) or more in diameter. Most frequently, the crystals growing within a geode are quartz, calcite, or fluorite, though occurrences of other minerals are found. These objects are prized by collectors for their well-formed crystals and outstanding beauty.

Geodes are typically characterized by an outer shell of chalcedony, a dense microcrystalline form of quartz. The hard outer shell of the geode can usually be separated from the enclosing rock material. Geodes are most often formed in limestone or volcanic rocks, though they are rarely found in mudstones. The mineralogy of the geode and the rock in which it formed are commonly different. Because chalcedony is often harder and more weather resistant than the host rock, the hollow spheres resist the effects of erosion and are left behind as the host rock is eroded. Collectors identify the geodes in the field based upon their shape, the characteristic chalcedony shell, and the lower density arising from the hollow center.

The initial requirement for the formation of a geode is the presence of a cavity in the host rock. In a volcanic rock, such voids are frequently a result of the release of gases from the molten lava. As the lava hardens, the gas bubbles are preserved as holes in the rock. In the cases of sedimentary rocks, such as limestone, a hole may develop as groundwater dissolves the rock itself or as a result of the decay of biologic material buried at the time of deposition of the sediments. Groundwater within the sediments then carries dissolved minerals, including silica, through the host rock and into the cavity. The chalcedony shell is formed first, only fully hardening after an extended period of time. Subsequent mineralized groundwater flow may then deposit additional layers of minerals within the void. These crystal growths form first on the walls of the shell and then grow toward the center, producing the distinctive crystalline interior of the geode. The formation of a geode with large crystals may require tens or hundreds of millions of years.

Some of the most spectacular geodes come from Brazil. Some of these may be as large as one meter in diameter and contain very large amethyst (purple quartz) crystals. Once found, the geodes are often cut open with a diamond-tipped saw blade and the cut surfaces of the sphere polished for display.

Geodesic [next]

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

over 3 years ago

Crystal X Mengatasi Keputihan
Keunggulan Produk Herbal Crystal X
Crystal X
Produk Terapi Untuk Suami Agar Istri Cepat Hamil
Cara Pemesanan Produk Crytal X
Cara Pemakaian Crystal X untuk Hasil Memuaskan
Crystal X Benar-Benar Aman
Khasiat Crystal X Merawat Organ Intim
Mengatasi Keputihan Dengan Crystal X
Peranan Crystal X Sebagai Pembunuh Bakteri Jahat
Fungsi Crystal X Untuk Memperlancar Menstruasi
Efek Samping Penggunaan Crystal X
Mengatasi Keputihan Dengan Crystal X
Cara Mengatasi Keputihan Tanpa Efek Samping

Vote down Vote up

over 4 years ago

This was interesting reading. I am looking for a collector to pruchase my geodes. I have some that are shown in some of the books on geodes and date very far back in history. I have a 1/2 of a geode that has some very unique black crystal spears in it. My sister has the other 1/2 of the geode. I would like to know what all the crystals are and how rare it is. We were told it was very rare and valuable and that a collector would value it greatly. Please contact me at my email address if you can help me.

Vote down Vote up

over 4 years ago

not helpful thanks a lot!

Vote down Vote up

7 months ago

I love learning about this stuff - it's fascinating! Here's another great article about how amethyst cathedrals are formed/created that your readers would probably enjoy: https://cosmiccuts.com/blogs/healing-stones-blog/an-astonishing-behind-the-scenes-look-at-the-amethyst-cathedral

Vote down Vote up

8 months ago

yeezy v 2の販売,환상 판매,La vendita Yeezy V2,Yeezy V2 de vente,En el mercado yeezy V2.
http://www.newyeezyv2.com/ Zebra Yeezy
http://www.newyeezyv2.com/ Yellow Yeezy
http://www.newyeezyv2.com/ Yeezysupply
http://www.newyeezyv2.com/ Yeezys Shoes
http://www.newyeezyv2.com/ Yeezys For Sale
http://www.newyeezyv2.com/ Yeezys Adidas
http://www.newyeezyv2.com/ Yeezys
http://www.newyeezyv2.com/ Yeezy Zebra
http://www.newyeezyv2.com/ Yeezy V2
http://www.newyeezyv2.com/ Yeezy Supply
http://www.newyeezyv2.com/ Yeezy Sale
http://www.newyeezyv2.com/ Yeezy Price
http://www.newyeezyv2.com/ Yeezy Pirate Black
http://www.newyeezyv2.com/ Yeezy Outlet
http://www.newyeezyv2.com/ Yeezy For Sale
http://www.newyeezyv2.com/ Yeezy Cream
http://www.newyeezyv2.com/ Yeezy Boost V2
http://www.newyeezyv2.com/ Yeezy Boost
http://www.newyeezyv2.com/ Yeezy Blue Tint
http://www.newyeezyv2.com/ Yeezy Blue
http://www.newyeezyv2.com/ Yeezy Beluga 2.0
http://www.newyeezyv2.com/ Yeezy Beluga
http://www.newyeezyv2.com/ Yeezy Adidas
http://www.newyeezyv2.com/ Yeezy 350 V2
http://www.newyeezyv2.com/ Yeezy 350 Boost V2
http://www.newyeezyv2.com/ Yeezy 2018
http://www.newyeezyv2.com/ Yeezy
http://www.newyeezyv2.com/ White Yeezys
http://www.newyeezyv2.com/ Where To Buy Yeezys
http://www.newyeezyv2.com/ Supreme Yeezy
http://www.newyeezyv2.com/ Real Yeezys
http://www.newyeezyv2.com/ New Yeezys
http://www.newyeezyv2.com/ New Yeezy V2
http://www.newyeezyv2.com/ New Yeezy
http://www.newyeezyv2.com/ Cheap Yeezy
http://www.newyeezyv2.com/ Blue Tint Yeezy
http://www.newyeezyv2.com/ Black Yeezys
http://www.newyeezyv2.com/ Black Yeezy
http://www.newyeezyv2.com/ Beluga Yeezy
http://www.newyeezyv2.com/ Adidas Yeezys
http://www.newyeezyv2.com/ Adidas Yeezy V2
http://www.newyeezyv2.com/ Adidas Yeezy Boost
http://www.newyeezyv2.com/ Adidas Yeezy Blue Tint
http://www.newyeezyv2.com/ Adidas Yeezy
http://www.newyeezyv2.com/ Adidas V2
http://www.yeezyv2sales.org/ Yeezy Zebra
http://www.yeezyv2sales.org/ Yeezy Yellow
http://www.yeezyv2sales.org/ Yeezy V2 Boost
http://www.yeezyv2sales.org/ Yeezy V2
http://www.yeezyv2sales.org/ Yeezy Sales
http://www.yeezyv2sales.org/ Yeezy V2 Sales
http://www.yeezyv2.top/ Yeezy V2 Boost
http://www.yeezyv2.top/ Yeezy V2
http://www.yeezyv2.top/ Yeezy Cream
http://www.yeezyv2.top/ Yeezy Boost V2
http://www.yeezyv2.top/ Yeezy Boost 750
http://www.yeezyv2.top/ Yeezy Boost 700
http://www.yeezysv2.co.uk/ Zebra Yeezys
http://www.yeezysv2.co.uk/ Zebra Yeezy
http://www.yeezysv2.co.uk/ Yellow Yeezy
http://www.yeezysv2.co.uk/ YeezySupply
http://www.yeezysv2.co.uk/ Yeezys Shoes
http://www.yeezysv2.co.uk/ Yeezys For Sale
http://www.yeezysv2.co.uk/ Yeezys UK
http://www.yeezysv2.co.uk/ Yeezys
http://www.yeezysv2.co.uk/ Yeezys V2
http://www.yeezyshoes.top/ Zebra Yeezys
http://www.yeezyshoes.top/ Yellow Yeezy
http://www.yeezyshoes.top/ Yeezy Shoes
http://www.yeezyshoes.top/ White Yeezys
http://www.yeezyshoes.top/ Adidas Shoes For Men
http://www.yeezyshoes.top/ Adidas Shoes
http://www.yeezyboost350v2outlet.com/ Yeezy For Sale
http://www.yeezyboost350v2outlet.com/ Yeezy Cream
http://www.yeezyboost350v2outlet.com/ Yeezy Boost 350 V2 Zebra
http://www.yeezyboost350v2outlet.com/ Yeezy Boost 350 V2 Outlet
http://www.yeezyboost350v2outlet.com/ Yeezy Boost 350 V2 Kaufen
http://www.yeezyboost350v2outlet.com/ Yeezy Boost 350 V2 Footlocker
http://www.yeezyboost350v2outlet.com/ Yeezy Boost 350 V2 Blue Tint
http://www.yeezyboost350v2outlet.com/ Yeezy Boost 350 V2 Beluga
http://www.yeezyboost350v2outlet.com/ Yeezy Boost 350 V2
http://www.yeezyboost350v2outlet.com/ Adidas Yeezy Boost 350 V2 Zebra
http://www.yeezyboost350v2outlet.com/ Adidas Yeezy Boost 350 V2
http://www.yeezyboost350v2outlet.com/ Adidas Yeezy Boost 350
http://www.yeezyboost350v2outlet.com/ Adidas Yeezy Boost
http://www.yeezy500.org/ Yeezy For Sale
http://www.yeezy500.org/ Yeezy Cream
http://www.yeezy500.org/ Yeezy Blue Tint
http://www.yeezy500.org/ Yeezy Blue
http://www.yeezy500.org/ Yeezy Beluga 2.0
http://www.yeezy500.org/ Yeezy Beluga
http://www.yeezy500.org/ Yeezy 750
http://www.yeezy500.org/ Yeezy 700
http://www.yeezy500.org/ Yeezy 500
http://www.yeezy500.org/ Yeezy 350 V2
http://www.yeezy500.org/ Yeezy 350 Boost V2
http://www.yeezy500.org/ Yeezy 350 Boost
http://www.yeezy500.org/ Yeezy 350
http://www.yeezy500.org/ Yeezy 2018
http://www.yeezy500.org/ Yeezy
http://www.yeezy500.org/ White Yeezys
http://www.yeezy500.org/ White Yeezy
http://www.yeezy500.org/ Where To Buy Yeezys
http://www.yeezy500.org/ Ultra Boost Adidas
http://www.yeezy500.org/ Ultra Boost 4.0
http://www.yeezy500.org/ Ultra Boost
http://www.yeezy500.org/ Supreme Yeezy
http://www.newyeezyv2.org/ Yeezy Yellow
http://www.newyeezyv2.org/ Yeezy V2 Boost
http://www.newyeezyv2.org/ Yeezy V2
http://www.newyeezyv2.org/ Yeezy Sale
http://www.newyeezyv2.org/ New Yeezys
http://www.newyeezyv2.org/ New Yeezy V2
http://www.newyeezyv2.org/ New Yeezy
http://www.ukmonclercoat.co.uk/ Uk Moncler Coat
http://www.ukmonclercoat.co.uk/ Uk Moncler
http://www.monclerukonline.co.uk/ Moncler Uk Online
http://www.monclerukonline.co.uk/ Moncler Uk
http://www.moncler-ukoutlet.co.uk/ Moncler Uk Outlet
http://www.moncler-ukoutlet.co.uk/ Moncler Uk
http://www.monclerjacketoutlets.co.uk/ Moncler Jacket Outlets
http://www.monclerjacketoutlets.co.uk/ Moncler Jacket
http://www.monclerukjackets.co.uk/ Moncler Uk Jackets
http://www.monclerukjackets.co.uk/ Moncler Jackets
http://www.canadagooseuk.org/ Goose Down Jackets
http://www.canadagooseuk.org/ Canada Goose Uk
http://www.usnfljerseys.us/ Nfl Jerseys
http://www.usnfljerseys.us/ Nfl Jersey Cheap
http://www.usnfljerseys.us/ Nfl Jersey
http://www.usnfljerseys.org/ Nfl Jersey Cheap
http://www.usnfljerseys.org/ Nfl Jersey
http://www.usnfljerseys.org/ Nfl Cheap Jerseys
http://www.uscheapnfljersey.com/ Cheap Nfl Jerseys
http://www.uscheapnfljersey.com/ Cheap Nfl Jersey
http://www.nfljerseyscheapsales.com/ Nhl Jerseys 2018
http://www.nfljerseyscheapsales.com/ Nfl Jerseys For Sale
http://www.nfljerseyscheapsales.com/ Nfl Jerseys Cheap
http://www.cheapnba.top/ Nba Jerseys Cheap
http://www.cheapnba.top/ Nba Jerseys 2018
http://www.cheapnba.top/ Nba Jerseys
http://www.uscheapjerseys.us.com/ Cheap Jerseys
http://www.uscheapjerseys.us.com/ Cheap Jersey 2018 Us
http://www.uscheapjerseys.us.com/ Cheap China Jerseys
http://www.air-max2018.com/ Air Max 2018
http://www.air-max2018.com/ 2018 Nike Air Max
http://www.air-max2018.com/ 2018 Air Max
http://www.nikeairvapormax.top/ Nike Vapormax
http://www.nikeairvapormax.top/ Nike Air Vapor Max
http://www.vapor-max.com/ Vapormax
http://www.vapor-max.com/ Vapor Max Nike
http://www.vapor-max.com/ Vapor Max
http://www.vapormax2018.org Vapormax 2018
http://www.vapormax2018.org Vapormax
http://www.vapormax2018.org Vapor Max Nike
http://www.vapormax2018.org Vapor Max
http://russia2018jersers.com/ 2018
http://russia2018jersers.com/ Worldcup 2018
http://russia2018jersers.com/ World Cup Soccer 2018
http://russia2018jersers.com/ World Cup Russia 2018
http://www.footballjerseycheap.com/ World Cup Russia
http://www.footballjerseycheap.com/ World Cup Football 2018
http://www.footballjerseycheap.com/ World Cup Football
http://www.footballjerseycheap.com/ World Cup 2018
http://www.warriors-gs.com/ Warriors Jersey
http://www.warriors-gs.com/ Nba Warriors
http://www.warriors-gs.com/ Golden State Warriors
http://www.michael-kors-bags.us/ Michael Kors Factory Sale
http://www.michael-kors-bags.us/ Michael Kors bags
http://www.michael-kors-bags.us/ Michael Kors
http://www.jordan-air.us/ Jordan Air
http://www.jordan-air.us/ Cheap Jordan Shoes
http://www.jordan-air.us/ Air Jordan Shoes
http://www.jordan-air.us/ Air Jordan
http://www.asics.us.com/ Asics Shoes
http://www.asics.us.com/ Asics
http://www.clearancefitflop.com/ Cheap Fitflop
http://www.clearancefitflop.com/ Fitflop Clearance
http://www.clearancefitflop.com/ Fitflop Sale Clearance
http://www.clearancefitflop.com/ Discount Fitflop
http://www.clearancefitflop.com/ Fitflop Outlet
http://www.clearancefitflop.com/ Fitflop Clearance Outlet
http://www.clearancefitflop.com/ Clearance Fitflop
http://www.pandorajewellerywholesale.co.uk/ Cheap Pandora Charms
http://www.pandorajewellerywholesale.co.uk/ Pandora Charms Sale Clearance
http://www.pandorajewellerywholesale.co.uk/ Pandora Charms
http://www.pandorajewellerywholesale.co.uk/ Wholesale Pandora Jewellery
http://www.pandorajewellerywholesale.co.uk/ Pandora Wholesale
http://www.pandorajewellerywholesale.co.uk/ Pandora Jewellery Wholesale
http://www.pandorajewellerywholesale.co.uk/ Pandora Jewelry
http://www.pandorajewellerywholesale.co.uk/ Pandora Outlet
http://www.pandorajewellerywholesale.co.uk/ Pandora Charms Outlet
http://www.pandorajewellerywholesale.co.uk/ Pandora Rings
http://www.pandorajewellerywholesale.co.uk/ Pandora Bracelets