The area has a wide variety of geological aspects to explore as well as fauna and flora so make a day of it.
This Earth Cache is a follow up on the Kini Baai Pebble Beach Earth Cache, looking at a Cobble.
The grain sizes of sediments and sedimentary rocks are a matter of great interest to geologists. They determine grain sizes in the field using printed cards called comparators, especially for the larger sizes. In the laboratory, comparators are supplemented by standard seives.
The Wentworth scale was published in 1922 by Chester K. Wentworth, modifying an earlier scale by Johan A. Udden. Wentworth's grades and sizes were later supplemented by William Krumbein's phi or logarithmic scale, which transforms the millimeter number by taking the negative of its logarithm in base 2 to yield simple whole numbers.
The size fraction larger than sand (granules, pebbles, cobbles and boulders) is collectively called gravel, and the size fraction smaller than sand (silt and clay) is collectively called mud.
A cobble is defined as a clast of rock with a particle size of 6.4 centimetres (2.5 in) to 25.6 centimetres (10.1 in) based on the Krumbein phi scale of sedimentology. Cobbles are generally considered to be larger than pebbles (4 to 64 millimetres diameter) and smaller than boulders (greater than 256 millimetres diameter). A rock made predominantly of cobbles is termed a conglomerate.
The Krumbein phi scale size ranges define limits of classes that are given names in the Wentworth scale (or Udden–Wentworth scale) used in mainly in the United States.
Below is the Krumbein Phi Scale:
Logging this Earth Cache:
To log this cache you have to answer the following questions and submit them by contacting me via my profile here: http://www.geocaching.com/profile/?guid=725aed9a-cab8-4487-88b1-e57698b634a8.
1) Describe the cobbles on the beach at ground zero referring to their color, texture, size and numbers?
2) What size must a rock be in order to be classified as a cobble?
3) At S 34° 2.243 E 25° 31.567 there is a memorial sign, what is written on the sign?
Sources: https://en.wikipedia.org/wiki/Cobble_(geology), http://geology.about.com/