Basaltsäule in Sankt Augustin EarthCache
Hidden : 1/13/2010
Difficulty:
1 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


Die Säule 1



Basalt ist ein basisches (SiO2-armes) Ergussgestein. Es besteht vor allem aus einer Mischung von Eisen- und Magnesium- Silikate mit Olivin und Pyroxen sowie calciumreichem Feldspat (Plagioklas). Basalt ist das vulkanische Äquivalent zum Gabbro (Plutonit), der die gleiche chemische Zusammensetzung hat.


Basalt entsteht, wenn dünnflüssiges, kieselsäurearmes Magma an der Erdoberfläche austritt und relativ schnell zu Basaltlava erkaltet.


Basalt ist für gewöhnlich dunkelgrau bis schwarz. Er besteht zum größten Teil aus einer feinkörnigen Grundmasse. Gröbere, mit bloßem Auge zu erkennende Einsprenglinge sind relativ selten, können aber bei einigen Basaltvarietäten häufiger vorkommen.

Die Erscheinungsform erkalteter basaltischer Lava ist hauptsächlich von zwei Faktoren abhängig. Eruptierte Lava kühlt recht schnell aus zu einem zusammenhängenden Gesteinsgefüge, das je nach Temperatur und Gasgehalt als Pahoehoe-Lava oder als Aa-Lava erstarrt. Findet die Abkühlung jedoch verzögert statt, entstehen durch das Zusammenziehen nicht selten meterlange eckige Basaltsäulen (Säulenbasalt), die sich senkrecht zur Abkühlungsfläche bilden, bevorzugt mit einer hexagonalen (sechseckigen) Geometrie.

Eine eher selten auftretende Erscheinungsform des Basaltes ist der Kugelbasalt, die man bevorzugt an Rändern von Basaltlagerstätten findet.

Die vielleicht bekannteste Formation aus Basaltsäulen findet man in Irland. Den Giants Causeway in Nordirland, der aus ca. 40.000 gleichmäßig geformten Säulen besteht.

In Sankt Augustin – Menden seht ihr eine Basaltsäule, welche in Dietz, im Westerwald, gefunden wurde.


Um diesen Cache zu loggen, beantwortet bitte folgende Fragen und schickt mir die Antworten per Mail und bitte nicht im Log:


1. Wie schwer ist die Säule?

2. Welche prozentuale Zusammensetzung von welchen Substanzen hat die Säule?




Die Säule 1


Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey.

On Earth, most basalt magmas have formed by decompression melting of the mantle. Basalt has also formed on Earth's Moon, Mars, Venus, and even on the asteroid Vesta. Source rocks for the partial melts probably include both peridotite and pyroxenite (e.g., Sobolev et al., 2007). The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below ocean ridges.

The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarse) groundmass are generally referred to as diabase (also called dolerite) or gabbro.


The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene. Olivine can also be a significant constituent. Accessory minerals present in relatively minor amounts include iron oxides and iron-titanium oxides, such as magnetite, ulvospinel, and ilmenite. Because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, and paleomagnetic studies have made extensive use of basalt.

In tholeiitic basalt, pyroxene (augite and orthopyroxene or pigeonite) and calcium-rich plagioclase are common phenocryst minerals. Olivine may also be a phenocryst, and when present, may have rims of pigeonite. The groundmass contains interstitial quartz or tridymite or cristobalite. Olivine tholeiite has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass.

Alkali basalts typically have mineral assemblages that lack orthopyroxene but contain olivine. Feldspar phenocrysts typically are labradorite to andesine in composition. Augite is rich in titanium compared to augite in tholeiitic basalt. Minerals such as alkali feldspar, leucite, nepheline, sodalite, phlogopite mica, and apatite may be present in the groundmass.

Basalt has high liquidus and solidus temperatures—values at the Earth's surface are near or above 1200 °C (liquidus) and near or below 1000 °C (solidus); these values are higher than those of other common igneous rocks.

The majority of tholeiites are formed at approximately 50–100 km depth within the mantle. Many alkali basalts may be formed at greater depths, perhaps as deep as 150–200 km. The origin of high-alumina basalt continues to be controversial, with interpretations that it is a primary melt and that instead it is derived from other basalt types.


During the cooling of a thick lava flow, contractional joints or fractures form. If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. The topology of the lateral shapes of these columns can broadly be classed as a random cellular network. These structures are often erroneously described as being predominantly hexagonal. In reality, the mean number of sides of all the columns in such a structure is indeed six (by geometrical definition), but polygons with three to twelve or more sides can be observed. Note that the size of the columns depends loosely on the rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns.

Perhaps the most famous basalt flow in the world is the Giant's Causeway on the northern coast of Ireland, in which the vertical joints form polygonal columns and give the impression of having been artificially constructed.



In Sankt Augustin – Menden you see a basalt column, it was found in Dietz in the Westerwald.


To log this earthcache, please give me an answer to this questions:


1. What is the weight of this column?

2. What is the chemical composition of this column (Percent and type)

3. Please make a picture of you with your GPS and send it with your log.

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