This Earth Cache is an example of Petrified Wood and is located in the Kirstenbosch National Botanical Gardens.
EDUCATIONAL LOGGING REQUIREMENTS
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For purposes of logging this cache you must answer the following four questions.
TO LOG THIS CACHE AND QUALIFY you need to answer the following questions in an email to the cache owner via our profile on the geocaching website. Any logs not accompanied by an email will be deleted.
1) At GZ there is a display of petrified wood. How old is the wood according to the display sign?
2) In your own words, describe how petrified wood is formed.
3) Based on the colours you see, what contaminant elements were involved in the formation of this petrified wood?
4)Are the trees that formed this petrified wood still growing in South Africa?
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Please do not post any images of the display sign. Logs containing these will be removed.
Petrified wood (from the Greek root petro meaning "rock" or "stone"; literally "wood turned into stone") is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree or tree-like plants having completely transitioned to stone by the process of permineralization. All the organic materials have been replaced with minerals (mostly a silicate, such as quartz), while retaining the original structure of the stem tissue. Unlike other types of fossils which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material. The petrifaction process occurs underground, when wood becomes buried under sediment and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition. Mineral-laden water flowing through the sediment deposits minerals in the plant's cells; as the plant's lignin and cellulose decay, a stone mould forms in its place. The organic matter needs to become petrified before it decomposes completely. A forest where such material has petrified becomes known as a petrified forest.
Some specimens of petrified wood are such accurate preservations that people do not realize they are fossils until they pick them up and are shocked by their weight. These specimens with near perfect preservation are unusual; however, specimens that exhibit clearly recognizable bark and woody structures are very common
Elements such as manganese, iron, and copper in the water/mud during the petrification process give petrified wood a variety of colour ranges. Pure quartz crystals are colourless, but when contaminants are added to the process the crystals take on a yellow, red, or other tint. The main contaminating elements with their related colour hues are:
- carbon – black
- cobalt – green/blue
- chromium – green/blue
- copper – green/blue
- iron oxides – red, brown, and yellow
- manganese – pink/orange
- manganese oxides – blackish/yellow
Petrified wood can preserve the original structure of the stem in all its detail, down to the microscopic level. Structures such as tree rings and the various tissues are often observed features.
Petrified wood is a fossil in which the organic remains have been replaced by minerals in the slow process of being replaced with stone. This petrification process generally results in a Quartz Chalcedony mineralization. Special rare conditions must be met in order for the fallen stem to be transformed into Fossil Wood or Petrified Wood. In general, the fallen plants get buried in an environment free of oxygen (anaerobic environment), which preserves the original plant structure and general appearance. The other conditions include a regular access to mineral rich water flowing through the tissues, replacing the organic plant structure with inorganic stone. The end result is petrified wood, a plant, with its original basic structure in place, replaced by stone. This process could occur in less than one thousand years. Exotic minerals allow the rare red and green hues that can be seen in more rare specimens.
Entrance fees
Adults:R75
SA Students (with card): R40
Children (6 - 17 years): R20
Under 6 years: Free
BOTSOC members: Free
SA Senior Citizens (with ID): Free on Tuesdays except on public holidays
Operational Hours
Sep-Mar (Summer) Mon-Sun 08h00-19h00
Apr-Aug (Winter) Mon-Sun
08h00-18h00
Conservatory Mon-Sun
09h00 -17h00