Seaton's Geodes EarthCache
Hidden : 2/12/2011
Difficulty:
2.5 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

How to log this cache
Using you GPS navigate to the listed coordinates. There you will find a small rock outcrop. Once you have found this rock you will be able to answer the following questions (Please email me your answers. Do not post with your found log):

1) Inspect one side of the rock. Estimate the density of the Geodes per square foot
2) What is the estimated diameter of the largest Geode in this outcrop?
3) Using the information provided in the cache listing what type of rock is most prominent in the Geodes?
4) Using the information provided in the cache pages, provide me an explanation (in your own words) on how geodes such as these are formed.
5) Using the information in the cache page would you say these formations are Nodules or Geodes?
6) (Optional) - Post a picture of you and\or you GPS at the cache site
7) (Mandatory) - Have fun... You are caching


What is a Geode?

A geode is a rock formation that combines minerals to form a hollowed-out rock with crystals lining the inside. It can take a long time for geodes to form. Some geodes that have been found are thousands to millions of years old. When a geode is split in half, the different layers can be seen, which will include the hollowed out center, crystal deposits and mineral deposits. If a geode is completely filled up with crystals leaving no hollowed space, it is called a nodule.

How are Geodes Made?

Geodes are made or formed by starting out in a hollow bubble inside a rock layer. Geodes formed from volcanic rock give us the best idea of of how a geode is made. Volcanic rock is formed from molten lava that cools and sets. When an air bubble appears, like those in pumice rocks, and slowly gets covered by more volcanic rock, the opportunity for a geode to form presents itself. This all happens while the air bubble is hot. When rain pelts down onto the outer layer of the rock, chemicals from the rock are released into the water. The water gets absorbed and passed through the hard, rocky outside layer of the bubble and then gets trapped on the inside of the bubble. This lasts for only a moment to a few seconds, long enough for the mineral-rich water to have small particles cling to the inside of the air bubble. Over time these particles turn into crystals from water constantly moving through the bubble and the water depositing more and more minerals to the inside of the hollow air bubble. Crystals of varying shapes and sizes appear depending on how long the geode has been forming and by how the water was moving through the air bubble. Geodes are also formed in hollowed-out animal burrows and also in hollowed-out tree roots.

Why are Geodes Different Colors?

When a geode is formed and then cracked open, we can see different crystal shapes, sizes and colors. Not all geodes are the same because of the different types of rocks that help them to form. The chemicals that the rocks release into the water that passes through the air bubbles is full of minerals. Different minerals that cling to the inside of the air bubble cause the different colors of crystal forming the geode. Most geodes have quartz or calcite that forms the interior because 90 percent of the Earth's crust is covered with silicates, which is exactly what quartz crystal is. Mix in some carbon and oxygen from the water passing through the air bubble and you have calcite. Colors appear when other minerals get mixed into the composition. Magnesium, iron and copper in a minute traces can change the colors in the crystals and also change the color variations in the crystal depending on whether they are mixed in with the quartz or with the calcite or both. Heat also plays a part in the colors that appear in a geode

What compounds are most prominent in Geodes??

Quartz belongs to the trigonal crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end. In nature quartz crystals are often twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals typically form in a 'bed' that has unconstrained growth into a void, but because the crystals must be attached at the other end to a matrix, only one termination pyramid is present. A quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward.
Calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar". Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form. Its fracture is conchoidal, but difficult to obtain.


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